Effects of dietary virginiamycin on performance and liver abscess incidence in feedlot cattle.

The effects of dietary virginiamycin level on performance and liver abscesses in feedlot cattle were evaluated in seven dose-response studies. Steers and heifers were fed finishing diets ranging in energy content from 1.34 to 1.51 Mcal of NEg/kg of DM. In all studies, virginiamycin added to the diet improved average daily gain and(or) feed conversion, with no substantial effect on dry matter intake. Pooled analyses of four studies providing virginiamycin at 11.0, 19.3, and 27.6 mg/kg of DM in the complete diet indicated that growth and feed conversion were linearly improved (P < .05); feeding 19.3 mg/kg improved these measurements by 3.0 and 3.8%, respectively. Overall incidence (score 0 vs score 1, 2, and 3) and severity (score 0, 1, and 2 vs score 3) of liver abscesses were reduced (P < .01) by feeding virginiamycin at either 19.3 or 27.6 mg/kg. Linear plateau modeling indicated that the effective dose range for virginiamycin in feedlot diets (DM basis) was 19.3 to 27.3 mg/kg for increasing average daily gain, 13.2 to 19.3 mg/kg for improving feed conversion, and 16.5 to 19.3 mg/kg for reducing liver abscess incidence.