EFFECTS OF VIRGINIAMYCIN ON THE PERFORMANCE OF PIGS FED BARLEY DIETS SUPPLEMENTED WITH SOYBEAN MEAL OR LOW-GLUCOSINOLATE RAPESEED MEAL

Ninety-six pigs, fed ad libitum from 10 to 94 kg liveweight, were used to examine the effects of including virginiamycin, at 0 and 1.102 g/100 kg diet, in starter and grower diets containing a low-glucosinolate rapeseed meal (Brassica napus L. cv. Tower) or soybean meal. Virginiamycin supplementation significantly increased growth rates, by 4.6% pre 33 kg liveweight and 5.1% subsequently, but produced a nonsignificant (P > 0.05) improvement in feed: gain ratios (2.8 and 0.5%, respectively). Use of the antibiotic did not significantly affect carcass criteria. Using the oilseed meals at 7.5% in the starter period and 12.5% subsequently, replacement of soybean meal by rapeseed meal resulted in a decrease in growth rates (from 546 to 518 g/day, P < 0.05, and from 754 to 706 g/day, P < 0.01, respectively) and poorer feed:gain ratios (2.38 vs. 2.51 kg feed/kg gain, P < 0.05, and 3.69 vs. 3.85, NS, respectively). Carcass differences between the pigs fed soybean meal or rapeseed meal were not significant (P > 0.05). The results suggest that the extent of the response to growth-promoting levels of virginiamycin may be influenced by dietary components.