Influence of tall fescue-legume mixed forages on ruminal volatile fatty acids of angus steers

Eight Angus steers involved in six standard digestion trials were used to evaluate the effects of variation in ratios of grass:legume forages, cutting date, dry matter intake, dry matter digestibility, and sampling time on ruminal production of volatile fatty acids (VFA) and ruminal pH. The grass portion of the forage was tall fescue (Festuca arundinacea, Schreb.), and legumes were crimson clover (Trifolium incarnatum) for Cutting Date 1, red clover (Trifolium pratense) for Cutting Dates 2,3, and 4, and Korean lespedeza (Lespedeza stipulacea) for Cutting Date 5. Samples were obtained via stomach tube and analyzed for volatile fatty acids by gas-liquid chromatography. Grass:legume ratios varied from 40:60 to 100:0, dry matter digestibility from 42% to 77%, and dry matter intake from 1.54 to 3.68 kg/day so there was wide variation that might affect VFA. Even with that diverse range of values, no more than 20% of the change in ruminal VFA could be explained by any one variable. In fact, many of the larger R² values were for relatively minor VFA. The lack of predictable variation in VFA ruled them out as important factors in animal performance differences between fescue-legume and pure fescue forages.