The effect of bentonite supplementation on ruminal protozoa density and wool growth in sheep either fed roughage based diets or grazing

Abstract

In penned sheep offered a mainly roughage diet, supplementation with 30, 50 or 60 g/day bentonite consistently increased the density of ruminal protozoa. The effect of 15 g/day bentonite administered via the drinking water to pregnant grazing ewes that were either normally faunated or had been defaunated for 6 months was studied. The wool growth of defaunated sheep at pasture was 25% greater (P < 0.05) than that of faunated animals. The wool growth of the latter was increased 17% (P < 0.15) by the addition of 15 g/day bentonite to their drinking water, while a similar addition of bentonite to defaunated sheep had no effect on wool growth. In this field study, supplementation with bentonite increased the population densities of protozoa free in the ruminal fluid of faunated sheep by 51% (5.6 X 105 v. 3.7 X 105, P<0.07). It is suggested that this allows a greater flow of protozoal protein from the rumen to the intestines, leading to increased wool growth in response to supplements of bentonite.