MODERATION OF RUMINAL FERMENTATION BY CILIATED PROTOZOA IN CATTLE FED A HIGH-GRAIN DIET

The objective of this study was to assess the influence of ciliated protozoa on ruminal fermentation in cattle fed high-grain diets. Six ruminally cannulated steers fed a corn-based grain diet (85% concentrate plus 15% alfalfa hay) at 12-h intervals were assigned randomly to two groups, ciliate free and faunated, in a crossover design. Defaunation was by ruminal emptying, omasal flushing, and treatment with sodium sulfosuccinate. Two to 3 weeks after defaunation, the ruminal contents of all steers were sampled before the morning feeding (0 h) and at 1, 2, 4, 6, 8, and 12 h after feeding to measure pH, analyze fermentation products, and monitor counts of ciliated protozoa and lactic acid-producing and -fermenting bacterial groups. Total numbers of ciliated protozoa in the faunated steers averaged 4.3 x 10(5)/g, and the protozoa consisted of nine genera. Ciliate-free steers had lower (P < 0.01) ruminal pHs (pH 5.97) than faunated cattle (pH 6.45); however, the treatment-time interaction was not significant. Ruminal lactate and ammonia concentrations were similar in both groups. The total volatile fatty acid concentration was higher (P < 0.05) in the ciliate-free steers than in the faunated steers and exhibited a treatment-time interaction (P < 0.05). The acetate-to-propionate ratio was higher (P < 0.05) in the faunated group than in the ciliate-free group and showed a treatment-time interaction (P < 0.05). Total anaerobic bacterial counts were about fourfold higher in the ciliate-free group than in the faunated group. Although counts of lactic acid producers were higher and counts of lactic acid fermenters were lower in ciliate-free steers than in faunated steers, the differences were not significant. Ciliated protozoa in cattle fed high-grain diets apparently moderate the ruminal fermentation rate as evidenced by higher ruminal pH values and lower volatile fatty acid concentrations in faunated cattle than in ciliate-free cattle. It appeared that the moderation of the ruminal fermentation rate by ciliated protozoa was attributable to reduced bacterial numbers and possibly reduced activity.