EFFECT OF DEFAUNATION ON FIBER DIGESTION IN SHEEP GIVEN 2 ISONITROGENOUS DIETS

The effect of defaunation on fibre digestion was examined in sheep given two isonitrogenous diets. One diet (L), which was composed mainly of pelleted lucerne (Medicago sativa) hay, had relatively low nitrogen solubility. The other diet (S), which was composed mainly of sodium hydroxide-treated wheat straw, had relatively high nitrogen solubility. Defaunation significantly reduced rumen fibre digestion. Reduction was larger with Diet L than with Diet S, and it was larger for the hemicellulose component than for the cellulosic component. Post-ruminal fibre digestion was increased by defaunation. Such an increase could compensate for reduced ruminal cellulose digestion, while it failed to compensate for reduced ruminal hemicellulose digestion. The results indicate the significance of rumen protozoa in hemicellulose digestion. The need for an adequate supply of non-protein nitrogen when animals are defaunated and receive low soluble protein is discussed. © 1990.