The effect of virginiamycin supplementation in sow diet on the reproductive performance of the gilt/sow

This trial investigated the effects of virginiamycin on sow and litter performance. Virginiamycin was added to the sow diet during the period of gestation and lactation at the levels of 0, 40 and 60 mg/kg, throughout two breeding cycles. Virginiamycin did not significantly affect sow weight change during gestation or lactation, or litter size and weight; there were no significant effects on food consumption (P > 0·05). However, when added at a level of 40 mg/kg virginiamycin tended to produce a better condition of sows which resulted in a significant reduction of replacement rate (P < 0·05), even though the proportion of gilts culled in the treated and untreated groups was high. The most evident result was a significantly shorter weaning-to-conception interval for the virginiamycin group at the end of the second reproductive cycle (first period, 5·9 days less than the control group, 2·5 days less than the 60 mg/kg group; second period, -9·5 days v. control group, P < 0·05, and -7·1 days v. 60 mg/kg group, P < 0·05), allowing a numerical improvement in productivity. Piglet performance was not significantly improved by the use of virginiamycin even though there was an evident trend in favour of the 40 mg/kg group which presented a higher proportion of heavier piglets (P < 0·05) and a reduction of pre-weaning mortality. A significant quadratic regression was found for weaning-to-conception interval and numeric productivity, indicating that the dosage more efficient to improve these parameters was 32 mg/kg. The results obtained in the virginiamycin 60 group were generally inferior to those of the 40 mg/kg group and also to the control group and seem to demonstrate that the 60 mg/kg dosage was too high.