Post weaning oestrus and luteal function in primiparous and pluriparous sows

The ovarian activity in 33 primiparous and 52 pluriparous post weaning sows was studied by progesterone determination. The progesterone profiles revealed that 90.4 per cent of the pluriparous and 66.7 per cent of the primiparous sows had resumed ovarian activity within 10 days. Ovulation within 10 days with overt oestrus occurred in 45.5 per cent of the primiparous and in 53.8 per cent of the pluriparous sows. Ovulation without detectable heat ('silent heat') occurred in 31 per cent of all sows during the first 10 days after weaning. The ability to resume ovarian activity was better in sows weaned in the period January to June than in sows weaned from July to December. Irregularities of luteal function were seldom observed in unmated sows. In mated sows which later proved to be non-pregnant, high progesterone values were common three weeks after mating.