Changes in feed intake and digestibility in sheep given virginiamycin

An experiment was conducted to investigate why virginiamycin reduces feed intake when it is first included in diets fed to sheep and cattle. Sheep were dosed daily with various amounts of virginiamycin, and measurements were made of both in vitro and in vivo dry matter digestibility and of blood gastrin concentrations. Virginiamycin decreased feed intake and there was some evidence that the effect was dose related. Dry matter digestibility was reduced by doses of virginiamycin >80 mg/day. Although highly correlated with feed intake, digestibility did not seem to be the sole factor influencing feed intake. Blood gastrin concentration was not significantly affected by virginiamycin and was not correlated with feed intake. Keywords: gastrin; ruminants