Effect of virginiamycin on ruminal fermentation in faunated or ciliate-free sheep overfed with barley grain

Abstract The effect of virginiamycin on ruminal fermentation was investigated in faunated or ciliate-free sheep challenge fed with 1.7 kg whole barley grain. Defaunation was achieved with oral drenching of alkanate 3SL3. All sheep were fed a diet of wheaten chaff (1.4 kg day −1 ) supplemented twice weekly with 700 g barley grain. The faunated ( n = 10) and ciliate-free ( n = 8) sheep were each randomly allocated to two treatment groups and challenge fed with 1.7 kg barley alone or with virginiamycin at 40 g per ton. Ruminal contents were sampled at 0, 1.5, 3.0, 6.0, 12.0, and 24 h after grain challenge to enumerate ciliated protozoa and measure pH and fermentation end-products. All animals consumed the 1.7 kg of grain within an hour of being fed. The inclusion of virginiamycin with barley decreased ( P Entodinium species. Defaunation had no effect on rumen pH, and concentrations of lactate, VFA, and ammonia. Sheep challenged with barley alone showed no evidence of ruminal acidosis (pH > 6.0 or lactate concentration P P P