Date of Award
Master of Science
Karl M. Barth
Robert R. Shrode, Charles S. Hobbs
The objective of this experiment was to determine which pasture quality measurements would be most accurate and most practical in combination with in vitro volatile fatty acid production after three specific periods of fermentation time in predicting body weight gains of beef animals grazing two types of pasture. A grazing trial had been conducted previously with steers on orchardgrass-clover and fescue-lespedeza pastures to determine changes in body weight gains throughout the growing season. Chemical composition (AIL, ADF, cellulose and crude protein content, and lignin:fiber ratio), visual estimates of forage species composition (percent grass, percent legume and legume index) and in vitro digestible dry matter of pasture samples had also been determined at 28-day intervals during the spring-summer grazing season. In the present study, an in vitro fermentation trial to determine VFA production was conducted with forage samples from these pastures, using 12, 24 and 36 hours of fermentation. Multiple regression equations were developed using measurements of pasture quality and in vitro VFA production. It was concluded that: 1. There is no combination of variables which can be used with 12-hour VFA production data which will accurately predict ADG of beef animals grazing either pasture species. 2. The combination of variables which explains the most variation in ADG of animals grazing OC pastures includes 24-hour molar percentage of butyric acid, acid insoluble lignin, percentage of fescue in the OC pasture, lignin:fiber ratio, percent cellulose and percent crude protein. The significant R2 (P<.01) indicates that this combination of variables accounts for 94 percent of the variation in ADG. For animals grazing FL pastures, the 24-hour equation using the combination of variables which accounted for the most variation in ADG yielded an R2 of .80 (P>.05), which was not as good as results following 36 hours of fermentation. 3. The combination of variables which most accurately estimates variation in ADG of animals grazing FL pastures includes 36-hour molar percentage butyric acid in combination with percent cellulose, legume index, percent fescue, in vitro digestible dry matter and percent crude protein. The significant R2 (P<.01) associated with this equation indicates that 91 percent of the variation in ADG of the cattle grazing FL pastures is accounted for by this combination of variables. For animals grazing OC pastures the 36-hour equation using the combination of variables which accounted for the greatest amount of variation in ADG yielded an R2 of .93 (P<.01) which was not as accurate as results from 24 hours of fermentation.
Shumway, Peter Eldon, "Volatile fatty acid production after different lengths of in vitro fermentation and its value as a predictor of the performance of grazing steers. " Master's Thesis, University of Tennessee, 1970.