THE INFLUENCE OF FOOD-INTAKE AND ALLYL TRENBOLONE ADMINISTRATION DURING LACTATION ON PLASMA STEROID CONCENTRATIONS AND THE REPRODUCTIVE-PERFORMANCE OF MULTIPAROUS SOWS

An experiment was made to examine the effects of food intake and an or ally active progestagen on plasma steroid concentrations and subsequen t reproductive performance of multiparous sows. Thirty-five multiparou s Landrace X Large White sows were assigned to one of four treatments immediately after parturition. Treatment H-AT sows were offered a high level of food intake throughout lactation: 3.5 kg of a diet containin g 160 g/kg dry matter (DM) of crude protein and 13 MJ digestible energ y per kg DM given twice daily. Treatment H+AT sows were offered the sa me food intake as H-AT sows and in addition they were given 20 mg/day of allyl trenbolone (AT) mixed with the morning feed. Treatment L-AT s ows were given 1.5 kg of the same diet offered twice daily during lact ation and treatment L+AT sows were also offered this lower level of fo od intake and given AT. The respective levels of food intake were offe red to sows from the 1st day of lactation onwards until weaning at 21 days post partum. Litter weights at weaning were influenced significan tly by feeding level (P < 0.001) and also by AT administration (P < 0. 05). Sows on the high level of feeding had the heaviest litters and fo od-restricted sows had the lightest litters. AT treatment depressed li tter weight at weaning. There was no effect of food level or AT on the plasma concentrations of progesterone or oestrogens during lactation, There was a highly significant (P < 0.001) difference in mean plasma oestrogen concentration between high (H-AT and H+AT) and low (L-AT and L+AT) fed groups during early pregnancy in the subsequent cycle. Sows given a combination of high energy in lactation and AT (H+AT) exhibit ed shorter intervals from weaning to oestrus than both groups of food- restricted (L-AT and L+AT) sows (P < 0.01) but treatment had no signif icant effect on either the farrowing rate or on the subsequent litter size. It is concluded that despite significant changes in the live wei ght and condition of sows and changes in steroid hormone concentration s due to food intake and the administration of allyl trenbolone, there were no significant effects on reproductive performance.