Masters Theses

Date of Award

8-2003

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Dr. Chris J. Richards

Committee Members

Dr. Gary Bates, Dr. John Waller

Abstract

In the midsouthern United States, forages exist as the major nutrient source for grazing beef cattle. A large forage base allows this region to produce and market many feeder calves to backgrounding and feedlot operations. The utilization of forage resources stands as a high priority to cattle producers. Supplementation of highly digestible fiber feedstuffs can be used to enhance animal performance, to take advantage of forage resources, and to extend forages by increasing stocking rates or increasing hay production. The development of forage based beef cattle finishing systems may be supported by high-fiber energy supplementation strategies. The availability of feeder cattle and an abundance of forage resources in the midsouth increase the feasibility for producers to develop an interest in forage fed beef, niche market opportunities. The objectives of the experiments conducted were: 1) to evaluate two forage based grazing systems designed to produce cattle finished to a traditional endpoint; 2) to determine the effects of soybean hull supplementation on forage intake and site and extent of nutrient digestion. Experiment one was replicated over two yr and consisted of 42 crossbred beef calves (305.3 ± 12.8 kg) of moderate frame size used to compare two forage-based beef cattle finishing systems. The calves were weaned each yr approximately twenty d prior to stratification by gender and weight, and allotment to each system. The cattle received no growth promoting implants or feed additives during the experiment. The two systems were: 1) cattle grazed on cool season perennial grass pastures and wintered on annual grass pastures (CSP+A) and 2) cattle grazed on cool season perennial grass pastures and wintered on stockpiled cool season perennial grass pastures with daily supplementation of pelleted soybean hulls at 1.0% BW on a dry matter basis (CSP+SH). There were three and four replications for CSP+A and CSP+SH, respectively. Each replication consisted of three steers and three heifers. Supplemented cattle were fed in bunks and all animals had free choice trace mineralized salt, access to fresh water, and sun shelter. The experimental grazing yr consisted of three grazing periods: fall, winter, and spring. Both systems were stocked at a rate of 4.9 calves/ha for each season with the exception of a winter stocking rate of 2.5 calves/ha for CSP+SH. The fall period consisted of both systems grazing cool season perennial grass paddocks. CSP+A cattle were then rotated to annual grass pastures while CSP+SH cattle were moved to stockpiled cool season perennial grass paddocks for the winter period. Hay harvested from CSP+SH experimental paddocks was fed to both systems when adequate winter forage was not available. Rotation back to the original fall paddocks occurred at the beginning of the spring period. The spring period lasted until the cattle were harvested. The mean of two consecutive d weights was recorded for the initiation of the experiment, each grazing period, and the end of the experiment. Corresponding to these weigh periods, ribeye area (REA) and back fat (BF) estimations were determined using real-time ultrasound. Twenty-eight d interval weights were recorded on cattle not withheld from forage or water, yet before daily supplementation to determine average daily gains (ADG) and to adjust soybean hull supplementation. Clipped forage samples were taken corresponding to every weigh period from five random locations (0.25 m2 x 2.54 cm) in each presently grazed paddock. Samples were used to determine forage quantity and quality. Masticated rumen samples were taken at the beginning of each grazing period from six fistulated steers equipped with rumen cannulas to determine diet quality selection. After 306 and 284 d (yr one and two, respectively) cattle were harvested and carcass data collected. The CSP+SH cattle gained 0.58 kg/d more (P < 0.01) than CSP+A cattle (0.40 and 0.98 kg/d, respectively), which resulted in 171 kg more total gain during the experiment. The CSP+SH cattle were heavier (P < 0.01) than CSP+A cattle at harvest (595.3 and 427.6 kg, respectively). CSP+SH cattle received an average of 1,139 kg/calf (DM basis) of soybean hulls throughout the experiment. Final carcass measurements indicated that CSP+SH cattle had a larger (P < 0.01) REA and thicker (P < 0.01) BF than CSP+A cattle (75.7 and 61.9 cm2; 1.00 and 0.25 cm, respectively). CSP+A cattle averaged a 1.4 yield grade (YG) and average Standard quality grade (QG), while CSP+SH cattle had a higher (P < 0.01) YG (2.8) and QG (low Choice). The CSP+SH system resulted in greater weight gains with higher quality carcasses than CSP+A. In the second experiment, six steers (289 ± 2 kg BW) fitted with ruminal and duodenal cannulas were used in a crossover design to evaluate intake and site and extent of nutrient digestion of fresh clipped endophyte infected tall fescue (Festuca arundinacea) pasture with or without soybean hull supplementation at 0.70% BW (DM basis). Steers were placed in metabolism units within an environmentally controlled room and provided with free choice access to fresh forage, water and a vitamin/mineral block. The spring growth of tall fescue was harvested daily for feeding during the experiment. Supplement was fed at 0700 just prior to feeding approximately 65% of the estimated daily forage. Additional forage was stored in a cooler and fed at 1900 to maintain a fresh forage supply. Experimental periods were 21 d with 15 d of adaptation and six d of sample collection. Chromic oxide (9 g) was dosed twice daily starting on d nine for use as a digesta flow marker. Duodenal samples were taken four times daily with times shifting one h each d to represent all h of a 24-h period. Soybean hull supplementation decreased (P < 0.05) forage intake from 1.79 to 1.56% BW, but increased (P < 0.01) total DMI from 1.79 to 2.21% BW. Apparent ruminal DM digestibility, 47.5%, was not affected (P > 0.35) by supplementation. Crude protein intake was 107 g/d greater (P < 0.04) with supplementation and duodenal CP flow for the supplemented treatment (782 g/d) was greater (P < 0.01) than the control treatment (569 g/d). Duodenal microbial CP flow was increased (P < 0.01) by 108 g/d with supplementation. Ruminal pH was not affected (6.5; P > 0.17) and ruminal ammonia nitrogen concentration was decreased (P < 0.03) from 3.7 to 2.3 mM with soybean hull supplementation. Total VFA concentrations (103.9 mM) were unaffected (P < 0.15). Rumen fluid dilution rate and fluid flow rate were not different between treatments (P > 0.60). Supplementation of soybean hulls at a rate of 0.70% BW to cattle consuming fresh tall fescue decreased forage consumption. Supplementation did not change the percentage of ruminal dry matter disappearance, but increased quantities of total tract nutrient disappearance. Also, the rumen conditions were maintained to support cellulolytic microbes and more N was converted to microbial crude protein with supplementation. The supplementation of soybean hulls in grazed forage diets improves overall diet digestibility, extends forage resources, improves animal performance, and provides an opportunity to produce a quality forage fed beef product.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS