Effects of beta-carotene and alpha-tocopherol on rumen bacteria in the utilization of long-chain fatty acids and cellulose.

Addition of safflower oil to a growth medium depressed the growth of mixed rumen bacteria above 200 mg/L and did not significantly increase bacteria, even at lower concentrations. However, when 10 mg/L of beta-carotene were added to 50 to 100 mg/L of safflower oil, bacterial growth was significantly increased. When more than 200 mg/L of safflower oil were present, beta-carotene markedly restored the growth capacity. alpha-Tocopherol was more effective than beta-carotene, although it inhibited growth at high concentrations. The combination of beta-carotene and alpha-tocopherol (each 5 mg/L) exerted partially additive effects. beta-Carotene plus alpha-tocopherol enhanced bacterial cell yield in the presence of safflower oil, caprate, stearate, or linoleate, suggesting that beta-carotene and alpha-tocopherol increase the utilization of fatty acids. beta-Carotene plus alpha-tocopherol also stimulated cellulose digestion in the presence of 100 mg/L of safflower oil, evidently through the increased growth of cellulolytic bacteria.