EFFECTS OF DIETARY VIRGINIAMYCIN ON PERFORMANCE AND LIVER-ABSCESS INCIDENCE IN FEEDLOT CATTLE

The effects of dietary virginiamycin level on performance and liver ab scesses in feedlot cattle were evaluated in seven dose-response studie s. Steers and heifers were fed finishing diets ranging in energy conte nt from 1.34 to 1.51 Meal of NEg/kg of DM. In all studies, virginiamyc in added to the diet improved average daily gain and(or) feed conversi on, with no substantial effect on dry matter intake. Pooled analyses o f four studies providing virginiamycin at 11.0, 19.3, and 27.6 mg/kg o f DM in the complete diet indicated that growth and feed conversion we re linearly improved (P < .05); feeding 19.3 mg/kg improved these meas urements 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 live r abscesses were reduced (P < .01) by feeding virginiamycin at either 19.3 or 27.6 mg/kg Linear plateau modeling indicated that the effectiv e 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 a bscess incidence.