EFFECTS OF BENTONITE ON WOOL GROWTH AND NITROGEN-METABOLISM IN FAUNA-FREE AND FAUNATED SHEEP

Two experiments were carried out with sheep that originated from a fauna-free flock and were fed a soybean meal-corn silage diet with or without a bentonite supplement. One-half of the sheep fed each diet in each experiment were faunated with a mixed population of ruminal protozoa, whereas the other half of the sheep remained fauna-free until the end of both experiments. Wool growth and daily gain were measured in Exp. 1. (eight rams per treatment), which lasted 110 d, and the metabolic effects in the rumen and intestinal tract of protozoa and dietary bentonite supplement were tested with cannulated wethers (four wethers per treatment) in Exp. 2. The results of Exp. 1 showed decreased wool growth (P < .05) due to the presence of protozoa in the rumen. Dietary supplementation with bentonite partly offset the decreased wool growth in sheep with protozoa, but there were no effects of dietary bentonite and no protozoa x bentonite interaction (P > .05). Daily gain was decreased by the dietary bentonite (P < .05) supplement but was not affected (P > .05) by the ruminal presence of protozoa. In Exp. 2, protozoa increased (P < .01) the ruminal concentrations of ammonia and decreased (P < .05) the acetic:propionic acid molar ratio. Fractionation of N in the duodenal digesta flowing from the stomach to the small intestine showed that protozoa decreased (P < .05) the flow of nonammonia N and bacterial N, and there was a protozoa x bentonite interaction for these effects (P < .05). The dietary bentonite supplement decreased (P < .05) the flow of protozoal N and tended to increase the flow of feed N (P = .17). The flow of total amino acids was increased by protozoa (P < .01), and there was a protozoa x bentonite interaction (P < .05), but amino acid flow was not affected (P > .05) by bentonite. The disappearance of N from the digestive tract was decreased by bentonite (P < .05), whereas the disappearance of OM and ADF was not affected (P > .05). The results of the two experiments indicate beneficial effects of the absence of ruminal protozoa or of dietary bentonite supplement in faunated sheep on wool growth. The results, however, indicate that the beneficial effect of bentonite supplementation is not associated with the increased supply of protozoal protein, but rather with the improved supply of feed and bacterial protein to the intestinal tract of sheep.