Masters Theses

Date of Award

8-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Karl Barth

Committee Members

H. A. Fribourg, J. B. McLaren

Abstract

Midland bermudagrass pastures consisting of Midland bermudagrass or Midland in combination with either tall fescue or legumes were compared to each other and to orchardgrass-clover or tall fescue pastures. The cage-and-strip method was used to determine forage consumption from the beginning of May until the beginning of September during 1975, 1976 and 1977. Yearling beef steers acquired from fall feeder calf sales and weighing an average of approximately 213 kg were used in a put-and-take grazing system. Tester steers were weighed at about 21-day intervals to determine rate of gain. All forage samples were assayed for total N and in vitro digestible dry matter (IVDDM). Estimated total digestible nutrients (ETDN) was calculated from IVDDM.

Three years of forage composition and intake data were reduced to polynomial equations describing the regression of ETDN and crude protein (CP) content and the intake of ETDN and CP, on elapsed days of grazing. The regression equations were used to generate predicted percentages of ETDN and CP and consumption of ETDN and CP at monthly intervals beginning on May 1 and extending to September 1.

The available forage of all the pastures decreased in ETDN content during the month of May with Mid + N and Mid + legumes forage exhibiting this decline throughout the grazing season. The %ETDN in available Mid + fescue, fescue and OG + clover changed little from June until pasture grazing was terminated.

Available Mid + legumes was the only pasture forage to increase in %CP from the beginning of the season, while all other pastures decreased in %CP. However, the decline of %CP in available Mid + N, Mid + fescue, fescue and OG + clover ended during early summer and began to increase. Only the pastures containing Midland forage decreased in CP content in late summer.

Consumed Mid + N, Mid + legumes. Mid + fescue and OG + clover forage decreased in ETDN content during May, with Mid + N and Mid + legumes continuing this trend throughout the season. Consumed Mid + fescue and OG + clover increased in %ETDN from July 1 until the animals were taken off. Fescue varied little in the ETDN content of consumed forage.

The %CP in consumed Mid + N and Mid + legumes decreased at about the same rate from May 1 to September 1. Consumed Mid + fescue, fescue and OG + clover increased in %CP throughout May. The CP content of consumed Mid + fescue and OG + clover were decreasing at season's end, while consumed fescue forage increased in %CP for the entire season.

Animals grazing Mid + fescue and Mid + legumes decreased their DM consumption/day for the entire season with Mid + legumes being consumed at a higher level in the beginning. Only in late spring and late August was Mid + N consumed at a greater level than either of the other two Midland treatments. Fescue DM consumption decreased steadily from May 1 to August 1, while OG + clover forage consumption increased from mid-May until late June preceded by a dramatic decrease.

Steer ETDN consumption/day decreased continuously from the beginning for all treatments except OG + clover which increased slowly from mid-May to mid-June followed by a significant decrease through July.

Fescue pastures allowed steers to consume levels of CP that were comparable to Mid + legumes without as rapid a decline, while steers on OG + clover increased CP consumption steadily until July when consumption levels decreased drastically.

Intake above maintenance data followed the same trends as consumption data.

Steer ETDN consumption per unit metabolic weight (gm/day) decreased throughout the season for all treatments.

Steers grazing Mid + legumes, Mid + fescue and fescue decreased their CP intake per unit metabolic weight by 25.3, 5 and 11.2 gm/day, respectively, over the course of the grazing season. Mid+N and OG + clover provided more CP consumption in late spring (16.4 gm/day) and early summer (17.8 gm/day, respectively) than any other time.

ETDN composition of available forage appeared to be more related to ADO than did CP composition. ADC did not appear to be related to the composition of consumed forage except for Mid + N pastures that demonstrated a rapid decline in both variables. ADG seemed to be most closely related to the consumption of ETDN and less related to CP and DM consumption.

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