To the Graduate Council:

1 am submitting herewith a thesis written by Mark A. Marsalis entitled "Effects of
Stocking Rate, Season, and Changes in Fungal Endophyte Level On
Performance of Steers Grazing Tall Fescue". I have examined the final copy of
this thesis for form and content and recommend that it be accepted in partial
fulfillment of the requirements for the degree of Master of Science, with a major
in Plant and Soil Sciences.

Henry A. Fribourg, Major Prpfessor

We have read this thesis and
Recommend its acceptance:

Accepted for the Council:

Interim Vice Provost and
Dean of the Gr^jjate School



EFFECTS OF STOCKING RATE, SEASON, AND CHANGES IN
FUNGAL ENDOPHYTE LEVEL ON PERFORMANCE OF STEERS

GRAZING TALL FESCUE

A Thesis

Presented for the
Master of Science

Degree
The University of Tennessee

Mark Alan Marsalis
December 2000



QOO^



Acknowledgments

I would like to offer my most sincere gratitude and indebtedness to the

following people for their assistance and support throughout the duration of my

graduate studies:

To Dr. Henry A. Fribourg, for serving as my major professor and for being

a steadfast mentor who never let me settle for anything less than perfection. His

shared knowledge and wisdom will remain with me forever, and for that I am

grateful.

To Dr. John C. Waller and Dr. John H. Reynolds, for serving on my

committee and for many hours of meaningful conversation and companionship. I

thank all of my committee for the assistance in the preparation of this thesis. In

addition, I am very grateful to Dr. Arnold M. Saxton, Marcella Mueller, Teri Ingle,

and Nancy Rohrbach for their statistical and technical assistance.

This research was partially funded by the Hobart Ames Foundation under

the terms of the will of the late Julia C. Ames. I wish to thank Marshall Smith,

Cornelius Dixon, and other Ames Plantation personnel for their assistance in

data collection and pasture and animal management.

To my fellow graduate students, Robert C. Gillis, James L. Klotz, and Paul

D. Ebner for their constant friendship and support which made me a stronger

person. I would like to thank especially A. Eugene Fisher for his assistance and

criticism on everything I have accomplished.



To my mother, who never let me give up on anything, pushed me to be a

better person, and whose support and caring will never be forgotten.

Finally, I would like to thank my wife, Karen M. Marsalis, who always

believed in me and whose love and patience helped me through it all.

Ill



Abstract

A study was conducted to evaluate steer performance on tall fescue

{Festuca arundinacea Schreb.) pastures with different Neotyphodium

coenophialum [(Morgan-Jones and Gams) Glenn, Bacon, and Hanlin]

endophyte infestation levels ranging from < 5 to > 80% and three stocking

densities (SD). Eighteen 1.2-ha pastures were grazed with newly weaned

Angus {Bos taurus L.) and Angus cross steers. Each pasture was assigned one

of four initial endophyte (E+) levels of about 0, 20, 40, and 80% infestation.

Steer and available forage weights were measured at 21-d intervals. Average

daily gain (ADG) and beef production for each season were 335 g d'^ and 100

kg ha ̂ for fall/winter, 480 g d"^ and 155 kg ha"^ for spring, and 260 g d"^ and 38

kg ha ̂ for summer, respectively. Seasonal ADG for fall/winter, spring, and

summer were 475, 556, and 297 for low SD; 286, 496, and 317 for medium SD;

242, 389, and 166 g d"^ for high SD. Increasing SD from low to high resulted in

decreased ADG due to low amounts of available forage at high SD. Decreases

in ADG and beef production per unit of E+ level increase were largest at high

SD, implying that E+ tall fescue plants increased in number more at high SD

than at low or medium SD, and that reduced gains may have been due to

increased proportions of E+ tall fescue ingested by steers as a result of E+ level

shift. Performance of steers grazing tall fescue pastures changing in E+ level

over four years was affected by SD and season interactions and varied with

treatment combinations.

IV



Table of Contents

Chapter Page

I. INTRODUCTION 1

II. LITERATURE REVIEW 5
Plant Morphology and Characteristics 5
Neotyphodium coenophialum and Ergopeptine Alkaloids 8
Effects of the Endophyte on Cattle Performance 11

A. Feed Intake by Cattle 12
B. Average Daily Gain 13
C. Beef Production 14
D. Prolactin/ Milk Production 14
E. Reproduction 15
F. Respiration/ Heart Rate/Vasoconstriction 16

Environmental Effects 16
Grazing and Stocking Rates 18
Endophyte Shift 21
Preference 23
Analysis Techniques 24
Breeds of Cattle 25
Management " 25

III. MATERIALS AND METHODS 30
General Procedures 30
Pasture Establishment 32
Animal Management 33
Data Collection 35
Statistical Analysis 37

IV. RESULTS AND DISCUSSION 38
Climate 33
Available Forage 40
Average Daily Gain . . . . . . . . . . . . . .43
Beef Production 49
Forage Quality 54
Prolactin 58
Endophyte Level Shift 60

V. CONCLUSIONS 65

LITERATURE CITED 68



Chapter Page

APPENDICES 75
Appendix A - Climatic Conditions 76
Appendix B - Available Forage 89
Appendix C - Total Live Weight 94
Appendix D - PAS-ELISA Procedure 99
Appendix E - Prolactin Protocol and Data 104

VITA. .111

VI



List of Tables

Table Page

1. Stocking densities in animals per 1.2 ha pasture, 1993-1997 30

2. Average daily gain least squares means of steers at three stocking
densities averaged over all seasons, 1993-1997 44

3. Average daily gain least squares means of steers during three
seasons averaged over all stocking densities, 1993-1997 44

4. Average daily gain least squares means of steers at three stocking
densities during three seasons over all E+ levels, 1993-1997 44

5. Beef production least squares means of steers at three stocking
densities averaged overall seasons, 1993-1997 50

6. Beef production least squares means of steers during three seasons
averaged overall stocking densities, 1993-1997 50

7. Beef production least squares means of steers at three stocking
densities during three seasons over all E+ levels, 1993-1997 50

8. Acid detergent fiber, neutral detergent fiber, and crude protein least
squares means of tall fescue during three seasons averaged over all
stocking densities and E+ levels, 1993-1997 55

VII



List of Figures

Figure Page

1. Adaptation of tall fescue in the United States 2

2. Influence of available forage on production per animal and per
acre of pasture 19

3. Map of experimental pastures 31

4. Average daily gain least squares means of steers at three
stocking densities overall E+ levels and seasons, 1993-1997 45

5. Computed effect of E+ level on average daily gain at three
stocking densities overall seasons, 1993-1997 47

6. Beef production least squares means of steers at three stocking
densities over all E+ levels and seasons, 1993-1997 51

7. Computed effect of E+ level on beef production at three stocking
densities over all seasons, 1993-1997 53

8. Acid detergent fiber (ADF) least squares means of tall fescue at
three stocking densities over all E+ levels and seasons, 1993-1997 56

9. Neutral detergent fiber (NDF) least squares means of tall fescue
at three stocking densities over all E+ levels and seasons, 1993-1997.. 57

10. Crude protein (CP) least squares means of tall fescue at three
stocking densities over all E+ levels and seasons, 1993-1997 59

11. Changes in E+ level from 1994 to 1997, by initial categories and
stocking densities 52

VIII



I. Introduction

Tall fescue is the predominant and most important cool-season grass in

Tennessee and grows in what is known as the 'fescue belt', between the northern

and southern regions of the United States (Figure 1). This transition zone is

located in the eastern U.S., from southern Illinois and Ohio south to northern

Mississippi and Georgia and from eastern Oklahoma east to the Virginia

Piedmont and the Carolines (Fribourg et al., 1991b). Tall fescue is desirable

because it is easily established, well adapted to a wide range of soils and pH

(4.5-8.0) and tolerates some pests and grazing abuse. The most widely grown

cultivar of tall fescue in the Southeast is 'Kentucky 31' (Hoveland et al., 1980).

Most of the approximately 1.5 million ha of tall fescue in Tennessee are used for

cattle grazing and non-agricultural purposes such as ornamental lawn and

roadside vegetative cover, recreational turf, and as a soil erosion preventative

(Fribourg et al., 1988). The majority of tall fescue grown in the Southeast is

infected with the endophytic fungus Neotyphodium coenophialum. This

endophyte is of interest to farmers and researchers for many reasons,

particularly the benefits it provides to the host tall fescue plant and the harm it

causes to cattle and horses grazing the infected fescue. Endophyte infected tall

fescue causes a condition in cattle known as tall fescue toxicosis (Paterson et al.,

1995). The signs of tall fescue toxicosis in cattle include decreased body weight

gains, milk production, conception rates, serum prolactin and ability to dissipate

body heat. This condition causes severe harm, not only to the cattle, but to the



1

■s w.

m
s

n
Figure 1. Adaptation of tall fescue in the United States.
(Adapted from: Fribourg et a!., 1991. Tenn. Farm Home Sci. 160.)

Well adapted, area of major use

Generally adapted, little use

Generally not adapted



3
agricultural economy. Estimated annual losses average about $1 billion in the

U.S. and about $100 million in Tennessee alone (Fribourg et al., 1997). The N.

coenophialum endophyte causes the tall fescue toxicosis via ergot-like alkaloids,

resulting in alterations of physiological mechanisms within the animal, most of

which are still unknown. In addition to tall fescue toxicosis, the conditions known

as fescue foot, bovine fat necrosis, and agalactia in horses are also associated

with the N. coenophialum fungus.

There are beneficial contributions of the endophyte to the host tall fescue

plant. The endophyte provides insect and disease tolerance, as well as tolerance

to soil nematodes, livestock overgrazing (Hill et al., 1991) and drought conditions.

Drought tolerance is especially important in the southern region where dry, hot

conditions are frequent in summer. The physiological mechanisms by which the

endophyte contributes to these tolerances and to plant persistence are unknown.

It is known, however, that absence of the endophyte from tall fescue results in

decreased plant performance and productivity (Bouton et al., 1993).

Much time and effort have gone into tall fescue research with respect to its

relationship with the endophytic fungus, problems associated with tall fescue

toxicosis and the benefits it provides to the plant. Research has been limited in

the area of stocking densities of cattle on tall fescue pastures with different levels

of endophyte infestation. Studies involving the shift of endophyte infestation

incidence overtime have also been very limited. Preliminary data have yielded

promising results. If it can be shown that varying SO and levels of endophyte

infestation affect steer performance and forage productivity consistently, then



scientists can begin to understand better the mechanisms by which N.

coenophialum interacts with its surrounding community.



II. Literature Review

Plant Morphology and Characteristics

Tall fescue is a perennial bunch grass belonging to the Bovinae section of

the Festuca genus of the Poaceae family. It grows in a tufted type pattern and

has tillers used for lateral expansion and the formation of new plants (Brock et

al., 1997). Tall fescue can form rhizomes for additional plant expansion, which

result in positioning to a better, more favorable area for growth. Rhizomes tend to

be numerous in the winter, decline in spring and increase in summer/autumn.

The rise and peak seasons of summer and autumn are the two that exert the

most stress on the plant, indicating that rhizomes are longer-lived and can

survive adverse conditions. Survivability of rhizomes is critical to plant expansion

(Brock et al., 1997). Rhizomes can be influenced by season and grazing

management. Several perennial species, including tall fescue, keep the apical

bud close to or below the soil surface, thus minimizing grazing damage.

Extensive grazing can reduce the number and ability of dormant buds to develop

into rhizomes. Greater numbers of rhizomes lead to increased plant

competitiveness and stand persistence. On the other hand, severe basal shading

and overcrowding reduce tillering activity. Thus, moderate grazing promotes

tillering and lateral expansion and leads to a thick, full stand. Infected tall fescue

is known to produce more plant material than its endophyte free (E-) counterpart

under drought conditions. Endophyte infected tall fescue has deeper growing



6

points (Hill et al., 1991), greater tillering activity in certain months of the year,

and will yield more dry matter (DM) than E- tall fescue, particularly in the fall

months after a severe summer drought (Bouton et al., 1993). Since

environmental conditions in the mid-South are normally an alternation of periods

of abundant rainfall and droughts, the drought tolerance contribution from the

endophyte is especially important (Gwinn et al., 1998). Tall fescue can be

stockpiled in late August through October and grazed from November to late

January (Fribourg et al., 1991b) and is well adapted to the upper South; E+ tall

fescue is somewhat adapted to the extreme boundaries of the lower South.

However, tall fescue stands infested at low incidence rates and E- tall fescue

stands may not be well adapted to the lower South, as was shown by Gates and

Wyatt (1989) who compared the adaptability of 'AU-Triumph' tall fescue to

'Marshall' annual ryegrass {Lolium multiflorum Lam.). Ryegrass outperformed the

tall fescue, suggesting that low endophyte tall fescue was not a profitable

alternative to other E- strains on the extreme edge of the 'fescue belt'. In

marginal areas, such as west central Alabama, E- tall fescue has been adequate

at providing much better stands than less well adapted species, such as AP-2

Phalaris (Phalaris aquatica L.) (Hoveland et al., 1980). The E- Kentucky 31

cultivar sustained higher stocking rates, animal grazing days, gain ha"^ and

average daily gain than did phalaris. The phalaris pastures contained more

weeds and were more summer dormant than the tall fescue pastures. Another

study, by Pederson and Joost (1989) in Louisiana, showed that highly infested

KY-31 and Georgia Jesup had great seedling vigor the first three months after



7

seeding, a characteristic which is important for initial establishment of the plant.

However, only the Jesup exhibited better long-term persistence with highly

infested levels (89% stand) than with lower levels of infestation (< 50% stand).

These different studies indicate that the range of adaptability of tall fescue varies

greatly and is dependent upon environmental conditions and the level of

endophyte infestation that is associated with the pasture.

In one experiment, cows grazing E- tall fescue/legume mixtures had

greater body weight gains and better body condition scores than those

consuming such forages as smooth bromegrass {Bromus inermis L.)/red clover

{Trifolium pratense L.) pasture mixtures or corn (Zea mays L.) crop residues.

This showed that E- tall fescue was a good quality forage, not only when

compared to E+ tall fescue, but to other forages/feeds as well (Hitz and Russell,

1998). Forage quality tests indicate that tall fescue at an early growth stage is an

excellent source of digestible DM, crude protein (CP) and minerals for grazing

animals. Endophyte-free tall fescue maintains adequate nutrients throughout the

grazing season, but nutrients may be highest at early maturity (McCracken et al.,

1993). Although percent bound N increases as the plant matures, neutral

detergent fiber (NOP), acid detergent fiber (ADF) and acid detergent lignin (ADL)

increase as the season progresses. In-vitro organic matter digestibility (IVOMD)

decreases with forage maturity. Nutrient composition of the plant can vary

between E- and E+ cultivars. Tall fescue containing the endophyte tends to yield

more DM than E- plants, especially during the fall (Hill et al., 1991). On the other

hand, Aldrich et al. (1993) reported that E+ plants had lower DM and organic



8

matter digestibility, less CP and higher concentrations of NDF than did E-

plants. Nevertheless, E+ tall fescue contains adequate nutrients for grazing

cattle. Unfortunately, the good quality of tall fescue is overshadowed by the

problems associated with the mutualistic N. coenophialum fungus (Schmidt and

Osborn, 1993).

Neotyphodium coenophialum and Ergopeptide Alkaloids

There are no outwardly visible signs of the N. coenophialum endophyte on

the tall fescue plant (Fribourg et al., 1988). The endophyte mycelia occur

between the plant cell walls and utilize nutrients taken up through the roots of the

plant (Fribourg et al., 1991b). It is possible that the endophyte must obtain the

nutrients via plant cell leakage and/or freeing of the nutrients from the cell wall

(Siegel, 1993). The endophyte uses the plant nutrients to synthesize secondary

metabolites known as alkaloids, which may help provide stress tolerances to the

plant. Neotyphodium coenophialum provides beneficial qualities to the plant,

especially in areas where tall fescue sustainability is marginal (Fribourg et al.,

1988). Ergovaline is the predominant ergopeptine alkaloid found in infected tall

fescue and is found at biologically active levels (Garner et al., 1993). Support for

the theory that ergopeptine alkaloids are the causative agents of tall fescue

toxicosis began as early as 1977 when Bacon et al. (1977) proposed that the

endophyte Epichloe typhina (Fries) Tulasne, later reclassified as Acremonium

coenophialum Morgan-Jones and Gams (1982), was related to tall fescue



9

toxicosis. The endophyte was later reclassified as Neotyphodium coenophialum

(Glenn et a!., 1996). Porter et al. (1979) isolated and identified ergot alkaloids

from the endophyte, suggesting that these alkaloids may have been the

causative agents of tall fescue toxicosis. The findings of Yates et al. (1985) of

high levels of ergopeptine alkaloids in E+ tall fescue extracts from pastures with

cattle suffering from fescue foot further supported the idea that these alkaloids

may be responsible for tall fescue toxicosis. The predominant alkaloid was

ergovaline. Ergovaline represents 84-97% of the total ergopeptine alkaloids

present in E+ tall fescue (Lyons et al., 1986). Endophyte free tall fescue contains

none of these alkaloids. Unfortunately, availability of ergovaline is very limited on

a commercial basis and it is expensive; until it can be produced economically so

that its effects can be studied directly, the role of this compound in tall fescue

toxicosis remains uncertain. Ergotamine tartrate can be used to simulate

ergovaline responses in cattle, and it is cheaper and more readily available than

ergovaline. Ergopeptine alkaloids are biosynthesized via acetate metabolism.

Acetate metabolism yields dimethylallylpyrophosphate, which combines with

tryptophan and yields lysergic acid. Lysergic acid, when combined with amides

and an amino group, produces ergopeptine (Garner et al., 1993). It has been

suggested that tryptophan, inorganic phosphorus and oxygen may be regulators

of ergot alkaloid synthesis. Since these findings, many additional studies have

further determined the role of ergopeptine as well as that of other alkaloids in

stress tolerance of plants and tall fescue toxicosis. The alkaloid lysergamide

(LAA) is also present in tall fescue in high quantities (~ 45% of that of ergovaline)



10

and has been shown to cause vasoconstriction, one of the effects of tall fescue

toxicosis in cattle (Oliver et al., 1993). It is suggested that loline alkaloids and

peramine are associated with deterrence of insects, whereas ergopeptine

alkaloids are related to tall fescue toxicosis. This may not be completely accurate

considering that many alkaloids may work in conjunction to result in specific

properties (Porter, 1995). Any one endophyte strain may contain several

genotypes with different compounds, which may impart varying methods of

resistance. A strain, for example, may be able to provide stress tolerance but

without the toxic compounds associated with toxicosis (Latch, 1993). Prestidge et

al. (1982) found that endophytes could impart stress tolerances to plants and that

the Acremonium lolii endophyte in perennial ryegrass {Lolium perenne L.) could

protect the plant from the Argentine stem weevil {Listronotus bonariensis

Kuschel) attack. Toxins and deterrents, such as peramine and ergopeptine

alkaloids, were produced and reduced insect herbivory. Other compounds are

known to cause insects to die prematurely or affect the insect at different stages

of its life cycle and its eating habits (Latch, 1993).

Concentrations of alkaloids can vary with changing environmental

conditions such as season, fertilizer application and temperatures. The

pyrrolizidine alkaloids N-acetyl and N-formyl loline were found in tall fescue at

greater concentrations in late spring and early summer, when tall fescue

toxicosis occurs most frequently, than in winter (Kennedy and Bush 1983). It is

suggested that the possible causes of concentration fluctuations are factors such

as soil moisture and fertility, air temperature and grazing pressure. The Festuca



11

X Lolium hybrid used by Kennedy and Bush (1983) had an endophyte

Infestation of > 99%. Moderate temperatures resulted in the highest alkaloid

concentration, whereas both high and low temperatures caused a decrease in

concentration. This suggested that soil moisture played a more vital role in

alkaloid accumulation than temperature, especially since DM accumulation

decreased and both N-acetyl and N-formyl loline concentrations increased with

moisture deficit (Kennedy and Bush 1983). In addition, Lyons et al. (1986)

showed that plants grown with higher N fertilization rates contained higher

ergopeptine alkaloid concentrations than those without fertilization.

Effects of the Endophyte on Cattle Performance

The endophytic fungus N. coenophiaium in tall fescue is associated with

the condition in cattle known as tall fescue toxicosis. The endophyte is also

responsible for conditions known as fescue foot and bovine fat necrosis (Schmidt

and Osborn, 1993). Fescue foot occurs during cold weather and is characterized

by a gangrenous infection of the feet and tail, and may lead to eventual sloughing

of the hooves or loss of the tail. Fescue foot can be induced with only a few days

of grazing E+ tall fescue and exposure to cold weather. Bovine fat necrosis

(liptomatosis) is characterized by masses of hard, necrotic fat in adipose tissue of

the abdominal cavity and can lead to digestive disorders in cattle. Townsend et

al. (1987) found that steers grazing high E+ tall fescue tended to convert more

fatty acids into saturated fatty acids than did steers grazing low E+ tall fescue.



12

Neither bovine fat necrosis nor fescue foot Is as detrimental to the cattle

Industry as tall fescue toxicosis. The effects of the latter are spread out over a

larger area and the Impact on agriculture Is felt on a much larger scale than the

two former conditions. An example of this Impact Is the perception that

Southeastern cattle are Inferior to cattle from other areas of the U.S. when sent

to the marketplace. Buyers discriminate against these cattle mostly because of

their rough halrcoat, poor appearance and lowered weights and weight gains

(Schmidt and Osborn, 1993). Other signs of tall fescue toxicosis are decreased

prolactin concentrations In blood serum, conception rates, feed Intake and beef

production, and Increased respiration rates, vasoconstrlctlon, urination and

salivation. Signs of tall fescue toxicosis have been observed with as little as 20%

endophyte Infestation (Gwinn et al., 1998).

A. Feed Intake by Cattle

It Is hypothesized that reduced performance Is linked to decreased DM

Intake. Osborn et al. (1992) showed that the main factor affecting weight loss on

E+ pastures was reduced Intake, yet at the same time some animals consuming

E+ tall fescue had Intake values above maintenance level; however, the animals

lost weight, suggesting that the fungus contributed to weight loss due to effects

other than Intake. Grazing steers on E- KY 31 pastures consumed about 20%

more forage than on E+ pastures (Fribourg et al., 1991b). Goetsch et al. (1987)

found that DM Intake decreased linearly as a percent of body weight, about a



13

0.0055% decrease for each 1% increase in infestation. Cattle grazing E+

pastures have been observed in the warm season to graze more during cooler

evenings and night hours rather than daytime hours, when they spent most of the

time standing in water or in the shade (Schmidt and Osborn, 1993). Often, the

result of this inactivity was lowered overall intake of forage.

B. Average Daily Gain

Average daily gain values are decreased as a result of the endophytic

fungus in a manner parallel to effects on intake. One study by Crawford et al.

(1989) resulted in a negative linear relationship between ADO (0.09 kg d"^) and

percent endophyte infestation (per 10%). These values were close to those

Stuedemann et al. (1988) reported as a 0.05 kg d'"" decrease per 10% infestation

increase. Schmidt and Osborn (1993), while studying replacement heifer ADG,

obtained results similar to those of Stuedemann et al. (1988), a 0.045-0.05 kg

decrease in ADG per 10% increase in infestation. These studies suggested that

the relationship between ADG and percent infestation was linear. In contrast,

Fribourg et al. (1991a) reported that the relationship was not linear and that lower

levels of infestation had a greater effect on ADG per unit increase than higher

levels, suggesting a possible critical level for tall fescue toxicosis. All of these

studies have led to a general 'rule of thumb' of about 0.05 kg decrease in ADG

per 10% increase in infestation or about 0.6-0.8 kg d'^ and 0.4-0.5 kg d'^ gain on

E- and E+ pastures, respectively.



14

C. Beef Production

Since ADG, combined with SD, results in a value for beef production, it is

fitting to discuss the two aspects of ADG and SD together. It is known that weight

gains per animal and per ha are lower on E+ than on E- pastures (Read and

Camp, 1986). Lowered ADG leads to decreased overall production per unit of

land. Hoveland et al. (1981) measured beef production of about 415 kg ha'^ and

ADG was about 0.5 kg d"^ on highly infected pastures; these were low values for

spring. The effect of beef production decrease is more severe in summer,

particularly at high SD (Degroote and Lefebvre, 1996) and is decreased further

by increasing levels of endophyte. Several E- cultivars such as E- KY 31,

Johnstone, Kenhy and AU-Triumph will yield adequate production per ha and

ADG values for steers grazing them as long as the grass stand can withstand the

grazing pressure (Fribourg et al., 1991b).

D. Prolactin/Milk Production

Prolactin is a hormone responsible for milk production in cows and it can

be significantly reduced by tall fescue toxicosis. Increasing endophyte infestation

will decrease blood serum prolactin levels considerably, indicating a linear effect

with E+ levels increasing from as low as 22% (Fribourg et al., 1991b). The

reduction of prolactin can affect the overall performance of the animal. Since

pituitary concentrations of prolactin are not reduced, it is thought that the toxic



15

compounds (alkaloids) produced by the endophyte act as an agonist to the

dopaminergic suppression of prolactin secretion at the D2-dopamine receptor

(Strickland et al., 1993). In addition, dopamine changes gut motility or alters

ruminal motility and suppresses blood flow to various organs, this leading to

decreased digestion and nutrient availability (Strickland et al., 1993; Thompson

and Stuedemann, 1993). Dopamine antagonists have increased prolactin levels

in cattle (Paterson et al., 1995). It is also thought that temperature has an effect

on prolactin levels, with reduced levels at higher temperatures. However, plasma

prolactin levels have been shown to decline regardless of environmental

conditions in tall fescue toxicosis situations (Aldrich et al., 1993).

E. Reproduction

Tall fescue toxicosis affects reproduction in cattle grazing E+ tall fescue.

Schmidt et al. (1986) reported that beef heifers raised on E- tall fescue had

calving rates of 96%, whereas those on E+ pastures had only 55% calving rates.

For each 10% increase in infestation, conception rates decreased 3.5% and daily

milk production decreased 1.05 kg. Another study indicated that calf crop

decreased from 80% (E-) to 50% (E+) and pre-weaning gains were significantly

lower on E+ than on E- pastures (Fribourg et al., 1991b).



16
F. Respiration Rate/ Heart Rate/ Vasoconstriction

The alkaloid lysergamide has vasoconstrictive properties and has a

greater effect on veins than arteries (Oliver et al., 1993). Steers in a hot

environment normally have high peripheral temperatures due to vasodilatation

and the dissipation of elevated core body heat. When steers have infected tall

fescue in their diet, the peripheral temperatures decrease, indicating a

vasoconstrictive activity and lack of heat dissipation to the extremities (Osborn et

al., 1992). High rectal temperatures and respiration rates are further evidence

that body temperatures are not being dissipated. Both are significantly high in

steers consuming infected tall fescue. Heart rates are commonly depressed in

cattle grazing E+ tall fescue and may be due to pressure exerted from

vasoconstriction. In contrast, Osborn et al. (1992) reported that in a controlled

environment, rectal temperatures and respiration rates were similar in steers

consuming both E- and E+ tall fescue. This study suggested a diet-environment

interaction and that high temperatures may have compounded the effects of the

endophyte.

Environmental Effects

Factors such as ambient temperature and drought play a major role in

compounding the effects of tall fescue toxicosis. Heat is probably the most

influential factor on tall fescue toxicosis. Animal performance reduction is greater



17

in spring and summer than In fall and winter (Fribourg et al., 1991b). Since

summer Is usually hot and dry, cattle already experience some stress and tall

fescue toxicosis only worsens the situation. Steers kept In a controlled

environment of 21°C were reported to have significantly higher feed Intake, lower

rectal temperatures and almost half the respiration rate of those kept In a hot

environment of 32°C (Osborn et al., 1992). Decreases In gain (ADG and beef

production) are more prominent In warmer months (April to June) and are

magnified because of the potential for greater gains, especially In spring, when

there are larger quantities of available forage. Hyperthermla, panting, salivation

and an Inability to adapt to high temperatures can be attributed to tall fescue

toxicosis (Schmidt and Osborn, 1993). This becomes even more Important when

moving cattle from cool environments to areas of high temperatures when they

are not adapted to such locations, e.g.. Western feedlots.

Droughts will cause great stress to tall fescue plants and the N.

coenophialum endophyte will help to alleviate this stress. Since alkaloid

accumulation Is Increased with drought stress. It can be hypothesized that this

Increase In alkaloid concentration contributes to more Intense tall fescue

toxicosis effects on cattle. Other environmental factors, such as acid rainfall and

greenhouse gases, are becoming a popular concern and may affect plant

tolerances. Since precipitation with pH less than 4.5 has been reported

throughout the eastern U.S. and addle soils are common, the need for an acid

tolerant species such as tall fescue Is warranted. Reynolds and Wolt (1989)

showed that orchardgrass {Dactylis glomerata L.) plants were affected more by



18

acidic rainfall than were tall fescue plants; and orchardgrass leaves were

damaged at a higher pH than tall fescue leaves. These results suggested that tall

fescue may have been more tolerant to adverse environmental conditions than

other species.

Grazing and Stocking Rates

Stocking density (grazing pressure) can have an effect on plant and

animal performance in tall fescue pasture systems, in many situations grazing

pressure is thought to be the main stress factor when environmental conditions

are mild (Gwinn et al., 1998). As stated earlier, grazing tall fescue will help

produce a thick, full stand by promoting tillering activity and lateral expansion as

long as the stand is not overgrazed (Brock et al., 1997). Moderate grazing is

usually preferred because it allows for stand expansion and limits mature, poor

quality grass from developing, but does not put too much stress on the grass.

Although old stems tend to be more resistant than young stems to microbial

degradation because of their high C;N ratio (Hume and Brock, 1997), it is this

aspect of mature growth that can limit animal performance. The manner in which

grazing pressure is related to forage availability and animal production is shown

in Figure 2 (Blaser et al., 1986). Bransby et al. (1988) observed that heavy

grazing of infected tall fescue yielded higher gains per ha than moderate or light

SD. This may have been due to the fact that lower SD allow for mature growth

and increased seedhead production. Seeds are known to have higher



 

o

<
k_

(U
Q.

0)
Q.

C
o

t3
D
T3
O

High

o Medium

"to
E
c

<

Low

Output per
Animal

Overgrazed Output per Acre

or

Low HighVery Low | Medium

Available Forage

Undergrazed

Figure 2. Influence of available forage on production per animal and per acre of pasture.
(Adapted from: R.E. Biaser. 1986. Virginia Agric. Exp. Stn. Bull. 86-7.)

CD



20
concentrations of the endophytic fungus than leaves. When coupled with poor

quality mature growth, ingestion of the seedheads will limit animal production.

The study reported by Bransby et al. (1988) was isolated and involved a short

study period, only an 84-d spring period at the southern extreme of the tall fescue

range. Effects across all seasons should be evaluated to determine which SD is

best. Other studies have shown that cattle grazing E+ tall fescue at a high SD

had reduced ADG (Hoveland et al., 1997) and decreased overall performance.

Tall fescue persistence can be adversely affected by increasing SD (Gates and

Wyatt, 1989), especially during extreme drought. Careful attention must be given

to pastures during summer and on the regional edges of tall fescue adaptability.

It is suggested that low-to-moderate SD is best on the extreme southern edge of

tall fescue adaptation. Anything higher than moderate SD may damage the stand

of grass and in turn, overall production. Continuous grazing has been shown to

yield more tillers and plants on a mean density basis, whereas rotational grazing

results in larger individual plants with more DM per plant than plants continuously

grazed (Hume and Brock, 1997). Total DM is lower in continuously grazed

pastures than in rotationally grazed pastures. It is thought that livestock grazing

creates a mosaic of areas with varying degrees of utilization. Cid and Brizuela

(1998) showed that areas grazed heavily contained less biomass per unit

surface, were more dense and had higher N concentrations than lightly utilized

patches. It seemed that cattle gained nutritional benefits from heavily utilized

patches. Regrowth was of better quality than mature growth and heavily utilized

patches had less live and dead biomass than lightly utilized patches, indicating



21

that grazing prevented residue cluttering. Nitrogen concentrations were 26%

higher in heavily utilized patches than in lightly utilized patches (Cid and Brizuela,

1998) due to the fact that grazing maintained short and young vegetation that

contained low C;N ratios. Defoliation may have initiated N uptake and

translocation to damaged leaves, leading to a better quality plant.

Endophyte Shift

There is some speculation over whether or not the N. coenophialum

endophyte infestation level increases overtime. Crawford et al. (1989) reported

little or no change in E+ level over a 2- to 3-year period. Other studies (Read and

Camp, 1986; Shelby and Dalrymple, 1993) observed a shift in E+ levels, more

prominent at low levels of initial infestation. Over a 4-year period, initial levels of

27% had increased to 84% and initial levels of 58% had increased to 92%. It was

calculated that the average annual increase in E+ level was about 4.1% for all

plots. Initially low E+ pastures may become highly infested due to a high mortality

rate for E- tillers or plants, and a high E+ survival rate. Endophyte free and high

E+ levels did not significantly change overtime. Stands with zero percent initial

levels began to show detectable levels, but this was attributed to contamination

by seeds from adjacent pastures (Shelby and Dalrymple, 1993). Endophyte free

stands became very sparse and needed to be reseeded. Regarding the effects of

mowing on the endophyte shift, mowing can be compared to grazing in that it



22

prevents seedhead formation and promotes the spread of the plant (increased

number of plants). It was found that mowing plots yielded more plants per m^

than unmown plots. Mowing and grazing promote tillering activity and the E+

plants can fill the gaps left behind by the dead E- plants. This was one possible

explanation of how the endophyte may have spread. Infestation level changes

may be due to enhanced survival of the E+ plants where competition for moisture

during drought is intense (Shelby and Dalrymple, 1993) and grazing pressure is

high. Since E+ plants are more drought tolerant than E- plants, lack of rainfall can

also contribute to endophyte shift. At the Highland Rim Experiment Station,

Springfield, IN, Thompson et al. (1989) showed that high E+ levels (60-75%)

had not changed much over 2 years, but low levels of around 30% had doubled

and 15% infestation had tripled, again emphasizing that low levels of E+ were

more apt to change over time than high levels. Fribourg et al. (1991a) found that

moderate-to-high SD affected infestation levels, particularly at medium (25-60%

E+) initial endophyte levels. Little or no change in E+ level was detected when

intermediate E+ level pastures were grazed at low pressure or in initially high

(80% E+) level pastures at all SD (Gwinn et al., 1998). In general, pastures of

60% E+ or higher do not change as dramatically as intermediate E+ level

pastures and highest percent change will result with medium to high SD. Few

significant changes have been observed at infestation levels of 35, 60, and 81%

(Fribourg et al., 1991a). Clearly, it is recognizable that there is a relationship

between SD and infestation rate on E+ pastures.



23

The N. coenophialum endophyte is very competitive, is incorporated

into the sexual reproductive cycle of the plant and is disseminated via the seed.

The endophyte is spread through the seed of the tall fescue plant and will lead to

infestation level increase if pastures are allowed to reach reproductive stages of

growth. In addition, cattle are vectors of the endophyte through their feces, which

contain infected seeds when the cattle are moved from E+ to E- pastures (Shelby

and Schmidt, 1991). It is suggested that a 3-d quarantine period be implemented

for an adequate removal of E+ seed from the animal digestive tract. One steer is

estimated to pass > 3,000 viable E+ seeds within 3 d of removal from an E+

pasture (Shelby and Schmidt, 1991).

Preference

Another area of uncertainty is the issue of whether or not cattle prefer

certain types of forage to others, and whether they can select between E+ and E-

plants. Fisher et al. (1999) indicated that cattle prefer hays cut later in the day to

those cut in the morning hours. This preference was attributed to the fact that PM

hays contained lower levels of fiber (ADF, NDF, cellulose and lignin) and higher

concentrations of total nonstructural carbohydrates (TNC), monosaccharides and

disaccharides than did AM hays. These carbohydrates tended to accumulate

throughout the day, and decreased fiber concentrations. This was one example

of how nutritive value may have influenced grazing habits. Another example was

when cattle frequently grazed the previously mentioned heavily utilized patches



24

(Cid and Brizuela, 1998). Since these patches were of better nutritive value,

the cattle may have been able to sense the difference and preferred the patches.

If cattle do show preference to specific grass growth stages, then it is possible

that they may prefer E- to E+ tall fescue. This preference would lead to an

decrease in clover and E- plants in E-/E+-clover pastures and an opportunity for

E+ plants to spread (vanSanten, 1992). Fribourg et al. (1991a) reported this to be

the case when clover populations decreased as percent infestation increased,

and suggested the cattle grazed more of the clover as E- plants decreased.

Research by vanSanten et al. (1991) showed similar results that supported this

theory.

Analysis Techniques

There are several different methods for the isolation of the ergopeptine

alkaloids, including colorimetric analysis, tandem mass spectrometry (MS/MS),

high-pressure liquid chromatography and enzyme immunoassays (Garner et al.,

1993). Immunoassays are widely accepted as highly sensitive indicators of

ergopeptine alkaloids and allow for rapid analysis of many samples at one time.

Endophyte infestation levels can be determined by enzyme linked

immunosorbent assay (ELISA) techniques by using about 12 tiller samples per

ha at any season of the year (Fribourg et al., 1991b: Savaryet al., 1990).

Sampling results of winter, spring, summer and fall are not different for detection

of E+ incidence in tall fescue (Thompson et al., 1989).



25
Breeds of Cattle

Certain species of cattle are better adapted to heat conditions than others

and may be less affected by the problems associated with tall fescue toxicosis.

Brahman-Angus {Bos indicus-Bos taurus) crosses have been shown to suffer

less of a decrease in ADG than the Angus breed, with ADG decreases of 14%

and 38%, respectively (McMurphy et al., 1990). When grazing E+ tall fescue in

Oklahoma, Brahman cross steers had no rise in rectal temperatures and gained

weight faster than Angus steers. Goetsch et al. (1988) observed similar results

with British cross (34% decrease in ADG) and Brahman cross cattle (21%

decrease in ADG). Another study (Mezzadra et al., 1992) indicated that breed

performance varied with SD. Average daily gain was higher for Limousin {Bos

taurus) crosses than for Angus cattle at a low SD, but the opposite was true at a

high SD. Beef production was highest at a SD of-3.5 animals ha'^ for Angus, but

was highest at a SD of -2.8 animals ha"^ for Limousin cattle. This study

suggested that smaller animals produced more meat under limited forage

conditions and that larger animals were more affected by declining forage

availability than smaller animals.

Management

Beef cattle production in the southeastern U.S. is inefficient because cattle

are grazing land that is not of prime grain crop growing status (Hoveland, 1986).



26

Production could be improved by better management, improved forages,

animal health programs and controlled breeding seasons. Better management

can improve several aspects of beef-forage systems such as cow-calf and

stocker operations. A timed, controlled breeding season will help to utilize

available forage during seasons of high forage production. Improved health care

with elaborate records may help minimize potential losses at all production

levels. Economical forage production calls for the selection of the proper species

of grass to match environmental conditions as well as the soil. Better fertilization

practices than those commonly used today and supplemental forage efficiency

improvement are also necessary for economical production. Even though E- tall

fescue requires a higher level of management than E+ tall fescue, it leads to

improved gains. The individual producer must weigh all of these options and

determine what is best for the situation at hand. The costs need to be spread

over a broad economic base by not putting too much emphasis on individual

animal needs at one level, but focusing on the systems that affect costs and

returns presently and in the future of the product lifetime. By incorporating

several systems together, the producer can substantially improve profitability.

Regarding pasture improvement, or renovation with legumes, Fribourg et al.

(1988) suggested that pastures with E+ levels less than 30% can be substantially

improved by the addition of clover (Trifolium sp.) and that this clover can offset

the effects of the endophyte and lead to satisfactory animal performance. It is

suggested that long-term ingestion of low levels of ergopeptide alkaloids causes

less acute effects of tall fescue toxicosis than do high levels of alkaloids. This,



27

coupled with clover diet dilution effects, can lead to considerably improved

animal performance. In contrast, pastures with 30% infestation or more should be

considered for reestablishment (Fribourg et al., 1988) since the effects of clover

are not as significant as those observed in pastures with < 30% infestation.

Nevertheless, grazing of E- tall fescue is the best method for avoiding tall fescue

toxicosis.

Adding alfalfa {Medicago sativa L.) in mixtures may decrease the effects

of tall fescue toxicosis some, but not as much as the use of E- tall fescue

(Hoveland et al., 1997). Taking into account that most pastures in the Southeast

are 60-90% infested and an infestation of 65% may cause as much as a 45-kg

loss over 150 d, reestablishment and renovation are very necessary if production

is to be improved. Ongoing research has shown that E- tall fescue can survive

and continue to produce under certain management conditions. Reestablishment

can be very difficult and costly, but long-term benefits and returns could outweigh

the initial costs. Hoveland et al. (1981) found that SD could be increased when

cattle grazed E+ tall fescue with the addition of Regal ladino white clover (7.

repens, L.), birdsfoot trefoil {Lotus comiculatus, L.) or N application. Increasing

the SD improved beef production and was highest (653 kg ha"^) on tall fescue-

clover pastures and lowest (420 kg ha'^) on tall fescue-N pastures with tall

fescue-trefoil pastures being intermediate (447 kg ha"Y Average daily gain

followed the same pattern, with tall fescue-clover being the highest (0.68 kg d"^)

and tall fescue-N the lowest (0.48 kg d"^). It seemed that clovers and legumes

replaced some E+ tall fescue intake of cattle and thus reduced the effects of the



28

endophyte. These results exemplify the benefits of legume addition to the diet

and how renovation is superior to N fertilization alone.

New stocking practices are becoming popular in various parts of the U.S.

Intensive-early-stocking (lES), for example, is thought to be more profitable than

season-long-stocking (SLS). Some studies (McCracken et al., 1993; Huffaker

and Wilen, 1991) showed that forage quality declined throughout the grazing

season and lES utilized the good quality forage early and heavily. The pastures

were then rested later in the season for regrowth. When nutrient decline was high

(mid-May to June) due to adverse environmental factors, lES was best, but when

nutrient decline was low (April to mid-May), SLS was a better way to maintain

profitability. Ruminal fermentation rate was high early in the tall fescue-growing

season and microbial growth was more than optimal at this time (McCracken et

al., 1993). This model did not take into account factors such as the endophyte-tall

fescue toxicosis interaction or many other variables. All variables must be

considered when adopting a grazing management strategy.

Future strategies for improved production and the elimination of tall fescue

toxicosis are promising. Novel endophytes are currently being produced which

provide benefits to the host tall fescue plant, but without the adverse effects on

cattle associated with tall fescue toxicosis. Rumen microflora manipulation is an

area of interest that attempts to detoxify or reduce harmful alkaloids. Finally, the

use of antidotes, vaccines and supplements provides promise in future

elimination of the tall fescue toxicosis. It was shown that chemicals such as

estradiol-17 p had a positive effect on ADG in summer months (Davenport et al..



29
1993). Mean yearly changes in endophyte infestation levels of about 14%

(Gwinn et al., 1998) indicate the urgency of improved management practices

needed to maintain E- pastures and help with the problem of inferior cattle

performance until the physiological mechanism(s) of the endophytic fungus and

its ergot alkaloids are understood (Davenport et al., 1993). Future practices must

be altered so that they incorporate new techniques to help curb the deleterious

effects of tall fescue toxicosis and the spread of the causative endophyte. Much

work is needed if the southeastern U.S. is going to improve its beef production

systems and eliminate the detrimental effects of the N. coenophialum endophyte.



30
III. Materials and Methods

General Procedures

This study was conducted from fall 1993 to summer 1997 at Ames

Plantation, Grand Junction, TN (35''6' N, 89''l3' W) specifically the Hancock

Place, and at the Departments of Plant and Soil Sciences, Entomology and Plant

Pathology, and Animal Science, University of Tennessee, Knoxville, TN. At Ames

Plantation, eighteen 1.2-ha pastures on a Memphis silt loam soil (fine-silty,

mixed, thermic, Typic Hapludalf) were assigned one of four initial tall fescue

endophyte infestation level treatments of about 0, 20, 40, and 80%. The pastures

were assigned also a low, medium or high SD, which were adjusted from season

to season each year depending on forage availability (Table 1). Six pastures of

each of the three SD were used. Each SD had at least one of each of the four

initial endophyte level treatments, except for the high SD (Figure 3). The 0%

initial E+ level was not planned to contain the high SD treatment, but was

assigned the high SD treatment after seeding mixtures were switched

unintentionally.

Table 1. Stocking densities in animals per 1.2 ha pasture, 1993-1997.

Grazing Season Low Medium High
FallAA/inter 2-3 3-4 4-5

Spring 3 4-5 6-7

Summer 2-3 3-4 5-6



 

 
 

 

 

31

AMES

PLANTATION

Steer Grazing
1994-1998

*Percentages refer to E+ level

*Lo\v, Medium and High
refer to stocking densities

t
42 28%,

NMed

41

4%
33 30% HLow

34

46%
32H
82%

Low

31

8%

Med

35 24% Hi

" 30 32% Hi

/ 36 84% Low 1 29 46% Low
/ 37 0% Hi

28 56% Hi

/ 38 78% Med
27 32% Med

/ 39 56% Med
26 6% Low

40 26% Low
25 30% Med

Figure 3. Map of experimental pastures.



32

Pastures of different endophyte infestation levels within a specific SD were

stocked with equal numbers of animals, regardless of pasture condition. Initial

treatments to specific pastures are shown on Figure 3.

Pasture Establishment

Prior to seeding, all vegetation was killed in 1990 by using 1.12 kg ha"^ of

glyphosate [A/-(phosphonomethyl)-glycine] and disking after the herbicide had

taken effect. 'Tifleaf 11' pearlmillet [Pennisetum americanum (L.) Leeke] was then

seeded in 15-cm rows at 30 kg ha"^ (Gwinn et al., 1998). After the pearlmillet was

grazed and hay was cut, the crop was removed and replaced in October by

winter wheat [Triticum aestivum (L.) emend. Thell.] seeded in 15-cm rows at 134

kg ha'^ The winter wheat was grazed in the fall and winter, and grain was

harvested in June 1991. A soybean [Glycine max (L.) Merr.] crop (Maturity

Group III) was used the following summer and then harvested for grain. Weather

conditions in 1990 resulted in less than desirable stands of 1990-91 winter wheat

and 1991 soybeans. Therefore, the process was repeated in 1991-92. Another

winter wheat crop was planted in the fall of 1991 and harvested in June 1992.

Prior to tall fescue seeding in the fall of 1992, the pastures were disked lightly

and sprayed with glyphosate in July. Although the two-year smother crop process

was not conventional practice, it was necessary to ensure that there were no

remaining tall fescue plants from previous stands.



33
Soil samples were taken from all potential pasture areas in fall 1992.

Agricultural limestone was applied when soil pH was less than 5.5. Fertilizer was

applied when soil tests showed low P or K levels. These fertilizers were applied

each winter and spring to provide medium levels of fertility. Pastures were also

fertilized with about 56 kg N ha-'' in early September and in the spring of each

year.

Pastures were seeded in September 1992 in 20-cm rows at about 17 kg

ha-^ using a no-till drill. All seed used was of the same genotype of 'Kentucky 3T

tall fescue grown at the Plant Sciences Unit of the Knoxville Experiment Station,

Knoxville, TN. Endophyte free and 80% E+ or greater pastures were seeded

using only E- seed and E+ seed, respectively. The two intermediate infestation

levels were obtained by using appropriate ratios by weight, adjusted for

germination. Uniform pasture stands were established by spring 1993 and were

grazed from March to September. Pastures were fertilized with 56 kg N ha*^ and

stockpiled (fertilized and allowed to accumulate growth) from early September to

early November.

Animal Management

The animals used in this experiment were mostly from the Ames

Plantation herd or purchased from privately owned herds having characteristics

(e.g., age, breed, and weight) similar to those of Ames Plantation. Ninety-six

steers that initially weighed between 227 and 273 kg were used each year.



34

Animals were put on pasture in early November at the appropriate fall/winter

SD (low = 2 to 3; medium = 3 to 4; high = 4 to 5). When insufficient forage

existed in fall/winter and summer seasons, the SD were reduced (low = 2;

medium = 3; high = 4). Cattle were fed range cubes (Co-Op Range Cubes,

Tennessee Farmers Cooperative, Lavergne, IN 37086) to provide maintenance

during times of insufficient or unavailable forage and to maintain appropriate SD.

Grazing was terminated when mean standing forage height in a specific

treatment was less than 2.5 cm. Forage heights ranged from about 13 to 46 cm,

10 to 20 cm, and 2.5 to 10 cm for low, medium, and high SD, respectively. All

extra animals needed to increase SD in spring were kept on separate tall fescue

pastures and maintained through fall/winter at performance levels similar to those

of steers on experimental pastures. Steers used in the fall/winter period were the

same ones used the following spring and summer periods. Extra steers were

added to the fall/winter animals to adjust for increasing SD in spring (low=3;

medium=4 to 5; high=6 to 7). Spring SD were reduced when the summer grazing

season began in late June/early July. All extra animals were fed a diet other than

tall fescue for at least 3 d prior to being added to experimental pastures to

prevent seed contamination from non-experimental pastures.

At the end of the summer period, steers were removed from the

experimental pastures. Pastures were stockpiled during the early fall of every

year to provide adequate available forage for the fall/winter grazing season.

All pastures were inspected daily to assure animals were in proper

pastures and to check the health of all animals. In addition, every pasture had a



35

windbreak available for the fall/winter season and shade for the spring and

summer seasons. Adequate water, salt and minerals were available for all

animals.

Data Collection

Steers were weighed at the beginning and end of each season and at 21-

d intervals during each season. Fall/winter grazing began as close as possible to

November 1 and continued until March. Spring season began in mid-March and

ended about July 1. Summer grazing lasted from July 1 to the end of August

each year.

Data were collected at 21-d intervals and included steer weights, strip

clippings and pasture scores. Weighing dates coincided with strip clippings and

pasture scoring dates during spring and summer. Strip clippings were used to

measure available forage and nine clippings were taken per 1.2-ha pasture. A

stratified random sampling method (Thompson et al., 1989) was used with 3.048

X 0.508 m strips and at a stubble height of 2.54 cm. Forage clippings were put

into bags for drying and were weighed when dry. Available forage (kg DM ha-'")

was calculated by taking the difference between the final bag weight and the

initial bag weight for a period. The mean weight of the nine strip clippings was

converted from kg per m^ to represent kg ha"^ Pasture scores were taken by two

trained individuals at the beginning and end of the fall/winter period and at 21-d

intervals during the spring and summer. Pasture scoring included minimum.



36

maximum and mean tali fescue heights, species composition and percent

ground cover. The minimum amount of available forage required for the grazing

animals was about 500 kg ha-'' (Degroote and Lefebvre, 1996).

Blood samples were collected on weighing dates closest to July 1. The

blood serum was analyzed for prolactin concentrations. Protocol for

radioimmunoassy analysis of prolactin is presented in Appendix E.

Weather data were recorded daily and included precipitation and minimum

and maximum air temperatures. These weather data were used to correlate with

animal performances and forage availability.

Neotyphodium coenophialum infestation levels were measured with the

PAS-ELISA procedure (Thompson et al., 1989) (Appendix D). Prior to seeding in

fall 1992, endophyte levels of the two seed lots (0 and 80%) to be mixed were

determined. Beginning in June 1993, tillers were collected by a stratified random

sampling method (Thompson et al., 1989) utilizing 50 sampling spots per

pasture, with one tiller from each sampling spot. Tiller samples were collected

only once a year, during summer (June to August), and frozen immediately in

liquid N and stored frozen until PAS-ELISA analysis.

Forage quality data were obtained by using near-infared reflectance (NIR)

technology (FOSS NIRSystems, Model 5000, Silver Spring, MD 20904) and were

analyzed for CP, ADF, NDF, and DM. Blood serum analyses, ELISA and NIR

were conducted in the laboratories of the Animal Science, Entomology and Plant

Pathology, and Plant and Soil Sciences departments. University of Tennessee,

Knoxville.



37

Statistical Analysis

Since all treatments were not assigned to every block, data were analyzed

using the Mixed Procedure of SAS (SAS, 1999). A randomized block design

(RBD) with a factorial arrangement was used. Average daily gain, beef

production and forage quality least squares means were generated, having SD

and season as treatments, year as a random block effect and E+ level as a

continuous regression within the model. An additional blocking factor was

assigned to groups of pastures based on previous knowledge of similar

characteristics such as soil fertility, drainage and previous production potential.

Least squares means were analyzed for differences within interaction

combinations of SD and season. Mean separation was obtained by Fisher's

protected LSD (Steel and Torrie, 1980).

Since E+ levels were determined only once per year in early summer,

fall/winter and spring levels had to be estimated. This was done by plotting the

summer test levels for a particular pasture and fitting a regression line to the E+

level points for the four years. An equation was produced from the line and used

to generate the estimated level for the pasture. A newly estimated E+ level for a

particular summer was assumed to remain at that level through the fall/winter

and spring seasons until a change in level was detected the following summer. In

addition, E+ level slope values were used to determine the effect of E+ levels on

ADG and beef production.



38

IV. Results and Discussion

Climate

The varying climatic conditions from 1993 to 1997 influenced the

management of the experimental pastures. During periods of low precipitation

and limited available forage, SD were reduced, but pastures were never

terminated completely on any pasture except in early 1995 and late spring 1997.

High SD pastures were terminated in 1995 and 1997 because of excessively low

available forage, inadequate stands, and the inability to maintain the steers

appropriately within the experimental protocol. Climatic data are presented in

Appendix A beginning with 1993 because the first fall/winter grazing season of

the experiment began in the fall of 1993.

The overall 4-year climatic conditions of precipitation and temperature

(maximum and minimum) were similar to the 30-year normal averages for

Bolivar, TN (35°16' N, 89°59' W). Average monthly precipitation totals (Appendix

A1) from 1993 to 1997 were at or above 30-year average totals except for the

months of February, April, August, November, and December. The largest

amounts of precipitation occurred during the spring months and averaged about

140 mm. When 30-year normal temperatures were compared to the 4-year

experimental period, both the mean maximum and minimum daily averages were

similar to the normal and only minor differences occurred (Appendices A2, A3).



39

During the 1993 calendar year there were precipitation deficits during

the spring and summer seasons that continued into the fall (Appendix A4).

Although the precipitation was below average, adequate tall fescue stands were

maintained and ready for experimental animals in November. Maximum daily

temperatures were similar to 30-year normals, but were above normal for July

and August (Appendix A5). Minimum temperatures were above normal in July

and August as well (Appendix A6).

In 1994, the months of January through July received more than adequate

amounts of rainfall and were almost twice as much as 30-year normals in June

and July. In contrast, August to December precipitation amounts were

considerably lower than average (Appendix A7). Nevertheless, available forage

for 1994 was maintained as adequate, except for the high SD and medium SD in

winter and early spring, where values dropped below 500 kg ha"^ (Appendix B1).

Maximum and minimum temperatures averaged above normal, particularly in

November and December (Appendices A8, A9).

The 1995 year exhibited several periods of precipitation deficit, including

January to early spring, June, September, October and December (Appendix

A10). As a result, available forage dropped considerably from January to early

spring, particularly at the high SD (Appendix B2). Since rainfall was large in July

and August, available forage was maintained above adequate levels throughout

the remainder of the year. Maximum and minimum temperatures were also high

for August, but low in November and December (Appendices A11, A12). The low



40
temperatures in these two months may have caused the very small amounts of

available forage for the 1995 winter period (Appendix B3).

In 1996, again there were precipitation deficits early in the year (Appendix

A13). This deficit from February to April, combined with below normal maximum

and minimum temperatures (Appendix A14, A15), caused a considerable

reduction in available forage (Appendix B3). As precipitation levels increased

from May to August, available forage increased.

The study was ended after the summer grazing season in 1997. Rainfall

was adequate through the first half of the year, but was deficient in July. March,

June and September had very large precipitation amounts (Appendix A16).

Temperatures were similar to normals and slightly cool in April and May

(Appendices A17, A18).

Although there were no extended periods of drought or extreme hot or

cold temperatures during the study, temporary fluctuations in climatic conditions

affected overall management of the pastures. Occasionally, tall fescue availability

was reduced and SD had to be adjusted accordingly, but no stands were

damaged irreparably because of drought or extreme temperatures except when

subjected to high SD.

Available Forage

Forage availability was analyzed as total DM at a particular sampling date

during all grazing seasons and over all SD. The quantities of forage are shown in



41

Appendices B1, B2, B3, and B4, for all years. The general pattern was that the

low SD resulted in the largest available forage, followed by the medium SD, and

the high SD resulted in the smallest amount of available forage. Overall,

fall/winter and summer seasons contained similar amounts of average available

forage, but the spring season amounts were much smaller, except for 1993. For

the low and medium SD, the spring season amounts were considerably smaller

than fall/winter and summer, but at the high SD, the difference was not as great.

The reason available forage quantities were so much smaller in spring

than in the other two grazing seasons was because more animals were put on

pasture to utilize the good quality and potentially abundant growth from April to

June. In addition, the spring grazing period contained the month of March, which

was not very favorable for tall fescue growth. Since the animals were eating the

forage, when the March weather was unfavorable, the resultant spring total

availability was decreased. Stocking rates were reduced in summer and

fall/winter seasons and as a result, available forage increased.

The 1993-1994 available forage (Appendix B1) shows that forage quantity

decreased as the fall/winter season progressed (from November to February)

into months with less favorable climatic conditions. High and medium SD values

indicate that available forage was below 500 kg ha"^ for several months

throughout the year. As climatic conditions became more favorable for growth

(April to early-June), forage growth increased. Rainfall was very high during the

early summer months, and resulted in adequate forage growth in the late

summer.



42

Due to the period of non-grazing (stockpiling of pastures) from late

September to mid-November, available forage increased to very large levels for

the fall/winter season of the 1994-1995 grazing year (Appendix B2). Low SO

pastures averaged about 4000 kg ha'^ at the beginning of the fall/winter season.

Although there was low rainfall for the season, warm temperatures during the

winter resulted in excellent tall fescue growth. High SD pastures dropped well

below 500 kg ha"^ into negligible amounts. This decrease was amplified by low

rainfall from January to April. From April to December, high SD pastures

averaged more available forage than medium and sometimes, low SD pastures.

This was a result of not grazing high SD pastures from January to the end of

March due to inadequate amounts of forage.

The forage quantities were expected to be large in the fall/winter season

of the 1995-1996 grazing year due to stockpiling, but were much smaller than in

the previous summer (Appendix B3). Although the pastures were not grazed from

the end of August to late December, the amount of forage was quite small for the

beginning of the new fall/winter grazing season. This could be attributed to the

high temperatures of the previous summer and the low temperatures during

November. Again, forage quantity decreased as the fall/winter season

progressed, and the decrease was amplified by below average precipitation and

temperatures from February to April, as well as increasing SD. As precipitation

levels increased from May to December, available forage increased.

The 1996-1997 grazing year (Appendix B4) followed similar fluctuating

patterns, but had larger fall/winter forage values than 1995-1996 due to warm



43

winter temperatures and adequate precipitation. High SD pastures were

terminated in the spring of 1997 because of inadequate available forage and

decreased stands. These pastures were not reincorporated into the remainder of

the experiment.

Average Daily Gain

When all SD were averaged over all seasons, the low SD resulted in the

largest ADG, medium SD was intermediate and high SD resulted in the smallest

ADG (Table 2). These results were all significantly different (P < 0.01). When

seasons were averaged over all SD, spring ADG was larger than that of

fall/winter and summer (Table 3). Seasonal differences were significant (P <

0.01). The interaction between SD and season showed that during the spring,

low SD differed significantly from the high SD, but not from the medium SD

(Table 4). Fall/winter ADG for low SD was significantly different from both the

medium and high SD. During summer, only the high SD was significantly

different from the other two SD. At the low SD, spring was significantly larger

than summer, but not fall/winter. Medium and high SD results showed that spring

ADG was significantly larger than both fall/winter and summer (Figure 4). All SD

by season interaction means were different at P < 0.01.



44

Table 2. Average daily gain least squares means of steers at three stocking
densities averaged over all seasons, 1993-1997.

Stocking Density ADG

g hd 'd '

Low 443®
Medium 367"
High 266®
stocking densities not sharing the same superscripts are significantly different at P < 0.01.
n = 72

Table 3. Average daily gain least squares means of steers during three
seasons averaged over all stocking densities, 1993-1997.

Season ADG

g hd 'd '

Fall/Winter 335"
Spring 480®
Summer 260®

n = 72

Table 4. Average daily gain least squares means of steers at three
stocking densities during three seasons, over all E+ levels, 1993-1997.
Season Stocking Density

Low Medium High
g hd"' d"^

Fall/Winter 475®^ 286"' 242^^®
Spring 556® 496®'' 389"®
Summer 297®" 317®" 166®
Seasons and SD not sharing the same superscripts are significantly different at P < 0.01.
n = 72 for each SD and season



45

600

500

400
0)

q" 300

200

ILowSD

700 -r-

100

Fall/Winter

I Medium SO

Spring

□ High SO

DC

cd
cdcd

de

Summer

Figure 4. Average daily gain least squares means of steers at three
stocking densities over all E+ levels and seasons, 1993-1997.

Seasons and SO not sharing the same superscripts are significantly different at
P<0.01.

n = 72 for each season



46

In general, as SD Increased, ADG decreased. This decrease was

attributed to small amounts of available forage at the medium and high SD. The

general pattern indicated that as available forage decreased, ADG decreased

also. Decline of ADG in times of adequate forage (e.g. summer) may have been

attributed to heat stress or the reduced intake by the steers caused by the

endophyte and associated alkaloids.

Based on the regression analysis of ADG over all years and seasons

(Figure 5), a one-unit increase in E+ level would result in a mean decrease in

ADG of 0.44 g d"\ or 4.4 g d'^ per 10% increase in infestation at medium SD.

This decrease in ADG was amplified to 40 g d"^ for every 10% increase in E+

level at the high SD. The ADG decrease for low SD was 14 g d"^ per 10%

increase in E+ level. The high SD value of 40 g d"^ was similar to results reported

by Stuedemann and Hoveland (1988) and Schmidt et al. (1993) of 40 to 50 g d"^

decrease in ADG per 10% increase in endophyte infestation. Crawford et al.

(1989) reported decreases in ADG of about 90 g d"^ per 10% E+ level increase.

Overall results for the four years indicated that the medium SD had less of

an effect on ADG decrease per unit of infestation than did the low SD (Figure 5),

although the low SD resulted in the largest ADG averaged over all seasons.

Since the low stocking density ADG were large, the seasonal changes

(decreases) that occurred from spring to summer were greater for the low SD

than for the medium SD. The large reduction in ADG at the high SD may have

been due to the changes in E+ level that occurred in the high SD pastures.



 

47

"Medium SD "Low SD ■High SD

400

350

300

'•0 250
0)

0 200
Q
<

150

100

50

0

n = 72 for each stocking density

0 10 20 30 40 50 60 70 80 90 100

E+ Level, %

Figure 5. Computed effect of E+ level on average daily gain at three
stocking densities overall seasons, 1993-1997.



48
Endophyte level Increased rapidly at the high SD, which could have resulted in

greater amounts of E+ plants and associated toxins ingested by the animal.

Over all seasons and pastures, medium SD was comparable to the low

SD for ADG for the entire grazing year. Low SD gain was greater than medium

SD in the spring, but was smaller than medium SD in the summer. These

differences were not significantly different (P < 0.01), indicating that low and

medium SD had similar effects on overall ADG during the spring and summer

seasons.

There were differences in ADG between low SD and medium SD for the

fall/winter season. When the animals consumed the stockpiled tall fescue, the

regrowth was less abundant in the fall/winter season (due to unfavorable climate

in winter) than in spring. Forage availability decreased as the fall/winter season

progressed. Increased SD (from low to medium) may have magnified the forage

decline in fall/winter and resulted in small ADG. In contrast, as the spring season

progressed, the forage availability increased. As a result, more animals per ha

were not as damaging to the tall fescue plants in the spring.

The high SD resulted consistently in small ADG in all seasons when

averaged over all pastures and years, probably because of less available forage.

High SD average daily gains were particularly small in the fall/winter and summer

seasons when tall fescue productivity was limited.



49
Beef Production

Beef production for a season was calculated by multiplying the ADG by the

number of animal grazing days (number of animals*number of days in the

season) of the pasture. Animal grazing days depended on SD and were thereby

different when SD were adjusted periodically for season and forage availability

changes.

When averaged over all seasons (Table 5), beef production was greatest

for the medium SD, intermediate for low SD and smallest for high SD (P < 0.05).

Seasonal beef production across all SD (Table 6) resulted in spring having the

largest beef production, followed by fall/winter and summer (P < 0.05). Seasonal

and SD interaction analysis indicated that although the average high SD over all

seasons was smallest in beef production (Table 7), the spring high SD yielded

the largest amount and was significantly greater than the low SD (Figure 6). This

was expected since more animals were put on pasture in the spring than in

fall/winter or summer and in larger increments for the high SD (4-5 increased to

6-7) than for the low (2-3 increased to 3) or medium SD (3-4 increased to 4-5).

Bertelsen et al. (1993) reported that beef production per ha increased as stocking

rate increased within a rotational grazing system, without sacrificing gain per

animal. Within the summer treatment, there were no significant differences

among SD.



50

Table 5. Beef production least squares means of steers at three stocking
densities averaged over all seasons, 1993-1997.

Stocking Density Beef Production
kg ha"^

Low 97"
Medium 108^
High 89^
stocking densities not sharing the same superscripts are significantly different at P < 0.05.
n= 72

Table 6. Beef Production least squares means of steers during three

Season Beef Production

kg ha'^

Fall/Winter 101"
Spring 155®
Summer 38"=

< 0.05.
n = 72

Table 7. Beef production least squares means of steers at three stocking
densities during three seasons, over all E+ levels, 1993-1997.

Season Stocking Density
Low Medium High

kg ha'^

Fall/Winter 131" 109" es""
Spring 127" 164® 174®
Summer 33" 52"^ 30^
Seasons and SD not sharing the same superscripts are significantly different at P < 0.05.
n = 72 for each SD and season



 � 

 

 

 

51

! BLowSD Medium SD □ High SD
1 . . . . - - — . . . -

n iw
£

» 120

■o
o
k.

Q.

o
o

CQ

100

■80
fti

60

40

20 «t.

Fall/Winter Spring Summer

Figure 6. Beef production least squares means of steers at three stocking
densities over all E+ levels and seasons, 1993-1997.

Seasons and SD not sharing the same superscripts are significantly different at
P < 0.05.

n = 72 for each season



52

The high SD resulted in the smallest beef production in fall/winter. The low SD

had the largest beef production. These results were opposite of those obtained in

spring. Since the increments between the SD were not as large in the fall/winter

as they were in spring, the high SD may not have had such a large positive effect

on beef production. This could explain why increasing SD had an overall

negative effect on beef production, particulariy when combined with lower CP

concentrations within the forage in the fall/winter compared to that of spring.

Regression analysis of beef production over all years indicated that a one-

unit increase in E+ level resulted in a mean decrease in beef production of 0.21

kg ha"\ or a 2.1 kg ha"^ reduction per 10% increase in E+ level at the medium SD

(Figure 7). The high SD magnified the decrease to a 10.2 kg ha"^ decline per

10% E+ level increase. Low SD resulted in about a 3.3 kg ha'^ decrease in beef

production.

The effect of increasing endophyte infestation on beef production was

similar to that of ADG. At the high SD, the decrease in beef production per unit of

E+ level increase was the greatest, but was the lowest at the medium SD. This

effect may be explained by the results of the fall/winter season. Since the beef

production for high SD in spring is so much larger than in fall/winter, the greatest

declining effect would be shifted toward the high SD. The opposite trend patterns

presented in Figure 6 for fall/winter and spring show how beef production was

largest in spring, but smallest in fail/winter. This change exemplifies the

significant decline within the high SD. The regressions were run over all seasons,

therefore changes between any two seasons would be reflected in the regression



 

53

70

m 20

"Medium SD "Low SD ■High 80

« 50 ^

40

30

n = 72 for each stocking density
i

0 ^

0 10 20 30 40 50 60 70 80 90 100

E+ Level, %

Figure 7. Computed effect of E+ level on beef production at
three stocking densities overall seasons, 1993-1997.



54

slopes. Spring beef production was far superior to that of fall/winter and

summer due to increased numbers of animals within each SD and high forage

production rates. Although the forage availability analyses indicated that spring

had the smallest amounts of available forage, it was due to increased animal

numbers and increased forage consumption. Total live weights of steers on

pasture are presented in Appendices C1, C2, C3, and C4 and tended to be

largest during the spring months and at the high SD because of increased

numbers of steers on pasture.

Forage Quality

Acid detergent fiber and NDF were expected to decrease within forage

samples in the spring because vegetative growth was abundant. Fiber

concentrations were smallest in the spring and largest in the summer. When

averaged over all SD, ADF concentrations were smallest in spring, intermediate

in fall/winter and highest in summer; these values were all different at P < 0.01

(Table 8). Neutral detergent fiber concentrations were similar among seasons

with the smallest for spring, intermediate for fall/winter and largest for summer (P

< 0.01). Interaction comparisons for SD and season are shown in Figures 8 and

9 for ADF and NDF, respectively. Stocking density had no significant effect on

fiber concentrations. Fiber content within the tall fescue plants was expected to

decline in spring due to increases in immature vegetative regrowth and fiber was

expected to increase in fall/winter and summer. Turner et al. (1996) reported



55

Table 8. Acid detergent fiber, neutral detergent fiber, and crude protein
least squares means of tall fescue during three seasons averaged over all
stocking densities and E+ levels, 1993-1997.

Season ADF NDF CP

%

FallA/Vinter 39.7" 71.1" 11.8"
Spring 38.5° 69.5° 14.9^
Summer 40.6^ 73.6^ 10.8°
Seasons within a column not sharing the same superscript are significantly different at P < 0.01.
n = 72 for each forage component.



� 

56

I Low SD Medium SD

5?

u."
Q
<

□ Higli SD
45

abc
40

35

30

25

20

15

10

Fall/Winter Spring Summer

Figure 8. Acid detergent fiber (ADF) least squares means of tall fescue at
three stocking densities overall E+ levels and seasons, 1993-1997.

Seasons and SD not sharing the same superscripts are significantly different at P < 0.01.
n = 72 for each season



57

ILowSD I Medium SD

UL
Q
z

Fall/Winter Spring

□ High SD
80

abde

70

60

50

■40 mi

m30

11
m20

10

Summer

Figure 9. Neutral detergent fiber (NDF) least squares means of tall fescue
at three stocking densities over all E+ levels and seasons, 1993-
1997.

Seasons and SD not sharing the same superscripts are significantly different at P < 0.01.
n = 72 for each season



58
decreasing fiber levels in tall fescue as the growing season progressed toward

spring. This was observed in our study for ADF and NDF, but the differences

were neither significant nor meaningful in relation to having an effect on forage

digestibility or animal performance.

The concentrations of CP were expected to increase tall fescue with

grazing pressure because of low C:N ratios (Cid and Brizuela, 1998). Crude

protein did increase to significantly high levels as SD increased in the fall/winter

and spring seasons (Figure 10). Averaged over all SD, the spring contained the

largest CP levels, followed by fall/winter and summer (Table 8). When averaged

over all seasons, only the high SD was different (P < 0.01).

All the forage quality analyses from this study indicated that spring was

the superior season for good tall fescue growth. Since season was a much

greater factor than SD in determining the overall quality of the plant, more

emphasis was put on season than on SD when relating forage quality to ADG or

beef production.

Prolactin

Prolactin concentrations were analyzed for only two years (1996 & 1997)

of the study because samples for the other years were lost due to a freezer

breakdown. Over these two years SD did not have an effect on prolactin

concentrations in the blood of steers grazing E+ tall fescue. In contrast,

increasing endophyte infestation levels did have an effect on prolactin

concentrations in July 1996. July 1997 results indicated no such relationship



59

ILowSD I Medium SD □ High SD

18 ^

Ifi n

14 -

1? 4
5?

in -
Q.
O

8 -

6

4 -

2

n 4

cd de de

Fall/Winter Spring Summer

Figure 10. Crude protein (CP) least squares means of tall fescue at three
stocking densities over all E+ levels and seasons, 1993-1997.

Seasons and SD not sharing the same superscripts are significantly different at P < 0.01.
n = 72 for each season



60
(Appendices E1, E2). Decreases In prolactin such as those shown in 1996

could become quite significant at endophyte infestation levels of 80-100%.

Goetsch et al. (1987) reported that prolactin decreased linearly (15, 11.2, 0.1,

0.8, and 0.0 ng mL"^) as endophyte infestation in tall fescue hay increased from 0

to 25, 50, 75, and 100% in the diet of dairy steers. Stamm et al. (1994) reported

similar results with increasing concentrations of ergovaline in the diet of beef

steers.

Endophyte Level Shift

Since endophyte infestation levels changed over the 3-year period, they

were considered results rather than planned methodology. It was necessary to

analyze E+ levels separately because of this. All pastures (except one) with initial

E+ levels of 8% or greater increased in percent infestation. The E+ level shift

analysis was used to define the change as it related to initial infestation and 80.

Endophyte level shifts were analyzed using the Mixed Procedure of SAS, but

differently from the previously mentioned variables (ADG, beef production, and

forage quality). Since E+ level shifts were dependent upon initial endophyte

infestation levels, original (seeded) E+ levels (0-8%, 24-32%, 46-56%, and 78-

84%) were entered into the model with SD as treatments. Year was no longer a

block, but was a repeated measures effect, making all individual pastures

identical across years. Means of the different groupings of original E+ level and



61
SD treatment interactions were analyzed for significant changes over all years.

Since 1994 E+ test levels were the same as those at seeding, any E+ level

change from 1994 was considered to be a change from the initial seeding level.

The endophyte shift analysis was based on estimates of E+ levels for individual

pastures and years derived from regression line equations for each pasture.

Pastures were grouped according to initial E+ levels and analyzed

statistically. Results are presented as percentages of E+ level infestation (Figure

11). The 1994 E+ levels were the same as seeded levels and were considered

the basis for E+ level changes.

It should be noted that all high SD and one medium SD-category

combinations contained only two years of data due to the previously described

pasture terminations.

The category A (0-8% E+) of initial endophyte level did not change much

over the 3-year period. The average increase over all SD was about 7% for all

three years or < 3% per year. These changes are considered negligible because

the PAS-ELISA procedure is accurate only within ± 5%. The medium SD yielded

the highest percent increase, which was due to an initial E+ level of 8%. The low

and high SD initial E+ levels were 0% and did not change at all.

The category B (24-32% E+) infestation level changes were significant for

low and high SD and were 23 and 28% for 3 and 2 years, respectively. The

medium SD resulted in an 11% increase. Category B averaged about an 8.5%

change per year over all SD. The reason why the medium SD resulted in a lower

E+ level shift than the low SD was because one pasture with a medium SD



 

  

 

a
>
o
_i

+
m

0)
O)
c
ra
X

O

100

90

80

70

60

50

40

30

20

10

_.-am r

. - Ar - "

. — -

A- • < — '■

- A- ■ "

© — J
© L

0"

——H

. — A-
am

— 1

A-
0"'

."-A-

\3r ^
.-am

. - A- ■ " ■ '

Ar ■

m ^ • 1 r
.J^

~ ■«" ■ A, Medium

—•—A, Low, High

—®—B, Low
— -A- - B, Medium

- -H - B, High

—®—C, Low
— -A- - c, Medium

- -B - C, High

—♦ D, Low

~ " D,Medium

1994 1995 1996 1997

Figure 11. Changes in E+ level, 1994-1997, by initial categories and stocking densities.
A,B,C,and D refer to initial E+ categories; and Low, Medium, and High refer to stocking densities.

O)
N)



63
treatment decreased in apparent infestation level and thus decreased the

average for the medium SD.

The category C (46-56% E+) shifts vi/ere evident and were the largest

among all categories. The low, medium and high SD yielded 5%, 21%, and 37%

increases over 3, 3, and 2 years, respectively. Averaged over all SD, the

increase was about 9% per year. The category C performed similarly to the

category B, but was affected more by the high SD than was the category B.

The category D (78-84% E+) was not complete in that there was no high

SD for this grouping. Originally, there was not supposed to be a high SD in the

category A but, during seeding, seed mixtures were switched and the 0% E+

level was put into a high SD pasture. This left the category D without a high SD

treatment. Medium and low SD resulted in similar E+ level shifts to one another,

and increased 14 and 15% over 3 years, respectively. The three-year average

total was about 9.7% for both SD, or 4.8% per year.

Overall results for E+ level shifts were consistent with previous research.

The study by Gwinn et al. (1998) used the same pastures and experimental

procedures as our study, but consisted of only the first two years of data (from

1994 to 1996). Our values are slightly different from those of Gwinn et al., but our

values take into account one additional year (1997), when significant E+ level

changes occurred. Shelby and Dalrymple (1993) reported changes of about 4%

per year. Our results indicated an 8-9% increase per year in E+ level when

pastures had initial infestation levels ranging from 24-56%, and little or no

change at E+ levels of 0 or > 80%. Thompson et al. (1989) indicated that 65-90%



64
E+ levels did not change much over 2 years, but 30% and 15% Initial E+ levels

had doubled and tripled, respectively. In contrast, Crawford et al. (1989) reported

that little or no change occurred in most of their endophyte infested pastures over

2 years. Our study indicated significant changes, some of which occurred within

the third year of the study. This indicates that more than 2 years of data may be

needed to assess accurately the E+ level shifts that occur in pastures grazed by

cattle.

This study indicated that cattle grazing pressure resulting from increasing

SD, and E+ tall fescue plant persistence were the causes of E+ level shifts.

Pastures were not allowed to mature to seed head growth stage, and animals

were fed non-fescue forages for 3 d prior to being switched from E+ to E-

pastures to prevent fecal E+ seed contamination (Gwinn et al. 1998). In addition,

prior to seeding the experimental pastures, all previous tall fescue growth had

been eliminated thoroughly. Although there were periods of temporary drought,

there were no extended periods of severe environmental stress on the pastures.

All of these reasons would lead to the belief that the E+ level shifts were caused

by factors other than environmental stress or seed contamination. This study

indicated that increasing SD had a significant effect on increasing E+ levels and

the effect was greatest at high stocking rates and for intermediate initial E+

levels. The grazing pressure may have eliminated less adapted E- plants and

thereby allowed the E+ plants to invade the empty spaces left by dead E- plants.



65
V. Conclusions

Climatic conditions affected the management of pastures from year to

year, particularly in times of drought or below or above normal temperatures.

Stocking densities were adjusted when tall fescue availability was low and some

pastures were temporarily withheld from grazing so that available forage could

increase to minimum requirement levels. No experimental pastures were

damaged permanently or terminated until the final spring and summer seasons,

when the high SD pastures were unable to produce enough forage to maintain

the grazing steers. Total forage quantities were never as large as they were the

first year of the experiment: and they progressively declined with each following

year. These results indicate that continuous grazing can damage tall fescue

stands permanently, particularly on E- and low E+ pastures and during periods of

drought.

Increasing SD from low to high resulted in decreased ADG. This was

attributed to decreased amounts of available forage at the high SD. In addition,

the decrease in ADG per unit of E+ level increase was largest at the high SD,

implying that E+ tall fescue plants increased in number more at the high SD than

at the low and medium SD. This may have caused reduced gains due to

increased amounts of E+ tall fescue ingested by the animals at the high SD.

Spring resulted in the largest ADG, followed by fall/winter and summer, and was

a result of increased forage production during spring with favorable climatic

conditions for tall fescue growth. In spring and summer seasons, the medium SD

average daily gains were comparable to those of the low SD. Only during



66
fall/winter were the low SD average daily gains significantly larger than those

of medium SD. This difference was attributed to the decline of good quality

stockpiled tall fescue during the fall/winter at medium and high SD. The low SD

resulted in the largest amounts of available forage and thus, the largest ADG.

Beef production was largest during the spring season and at the medium

SD overall. As SD increased, beef production increased, except during

fall/winter. Having large amounts of stockpiled tall fescue for fall/winter at the low

SD produced the largest amounts of beef ha'\ Only during the spring was the

high SD the best method for beef production. Fall/winter and summer were not

good seasons for the high SD treatment due to rapidly decreased available

forage and these combinations resulted in the smallest amount of beef ha'V

Similar to the ADG results, the beef production decrease per unit increase in E+

level was greatest at the high SD. This may have been also attributed to a more

significant shift in E+ level at the high SD than at the low and medium SD, or

because of the significant decline in beef production from spring to summer and

fall/winter.

Forage quality was affected by season and was consistent with that

reported in the literature. Both ADF and NDF concentrations were largest in

summer, intermediate in fall/winter and smallest in spring. Although these

differences were significant statistically, they were small and not thought to have

had much of an effect on forage digestibility or animal performance in this study.

Crude protein was affected by both season and SD. Spring resulted in the largest

concentrations of CP and summer resulted in the lowest. These data supported



67
the concept that quality of tall fescue declined as the growing season

progressed, even though the plants were not permitted to develop to

reproductive stage. Since the high SD contained the largest concentrations of CP

during spring and fall/winter, this concept was further supported and Implied that

since grazing pressure was Increased, mature growth was Inhibited greatly.

Prolactin concentrations were affected by Increasing E+ levels and

resulted In an Inverse relationship In 1996. Although these results were limited to

only two years of the study, they Indicated that prolactin may have been a useful

marker In detecting the effects of N. coenophialum and the associated alkaloid,

ergovallne, on grazing cattle. Since prolactin concentrations are highly variable

and dependent upon many factors, more than one sampling per year Is required

to assess accurately the effects of E+ level on hormonal concentrations In cattle

grazing E+ tall fescue.

Increasing SD significantly shifted E+ levels from Initial (seeding) levels to

more highly Infested levels over the 3+-year period. Intermediate Initial E+ level

pastures (24-56%) were affected the most by Increasing SD, and 0 and > 80%

E+ level pastures were affected very little. These results Indicate the urgency of

proper management of tall fescue pastures and suggest that pastures containing

E+ tall fescue may have different E+ levels from year to year, resulting In altered

cattle performance.



68

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69

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