Vitamin E is not degraded by ruminal microorganisms: assessment with ruminal contents from a steer fed a high-concentrate diet.

Using an in vitro incubation system containing undiluted ruminal contents from a steer fed a high-concentrate, corn-based diet, we examined microbial degradation of DL-alpha-tocopherol acetate (TA). Gas production, pH, and fermentation acid profiles were done in an initial experiment to ensure conditions for reproducible, viable cultures over 24 h. The pH decreased from 5.7 to 4.9, gas production averaged 3.4 mL/mL of ruminal contents, and > 300 mM fermentation acids were produced. We then monitored the fate of TA added to bottles containing ruminal contents. Three methods of TA extraction were tried, of which two were used in experiments. The two methods used were 1) hot ethanol in a Soxhlet apparatus and 2) chloroform/methanol. Each of these was used to extract added TA from a set of three in vitro experiments. Concentrations of TA were determined at 0 h and after 4, 8, and 24 h at 39 degrees C. In the three hot ethanol extracted experiments, TA recoveries were 85% at 0 h. With time of incubation, TA levels either 1) remained constant, 2) decreased then returned to the initial value, or 3) decreased by approximately 50%. These inconsistent results indicated that this extraction method was unacceptable. In the latter three experiments we used a chloroform/methanol extraction method. Recoveries of added TA averaged 96% overall. Thus, the level of TA remained constant during the 24-h period, suggesting that microbial destruction of TA does not occur. Rather, the previously reported losses of vitamin E may be attributable to incomplete extraction of tocopherol from high-concentrate ruminal contents.