Influence of oral administration of allyl trenbolone on subsequent litter size of primiparous sows

Abstract Sixty-eight primiparous sows from 3 farms were used in 2 experiments. In experiment 1, 14 Large White and 14 Landrace sows were either fed allyl trenbolone at a rate of 30 mg/day for the last 10 days of a 28-day lactation or served as untreated controls. There was no treatment effect on the number of sows showing oestrus, the weaning-oestrus interval, synchronisation of oestrus, or conception rate after first service. Mean litter size at birth in treated sows was increased, but not significantly so (P > 0.05), by 0.7 live pigs per litter. In experiment 2, 40 crossbred sows of Large White/Landrace breeding on two farms were either fed allyl trenbolone at 30 mg daily for the first 7 days after weaning or were untreated controls. Treated sows had only a slightly longer weaning- mating interval and the onset of oestrus was more synchronous. No oestrous behaviour was noted during treatment with the progestagen and there was no effect on the number of sows eventually displaying oestrus, or conception r...