FACTORS AFFECTING THE ONSET OF PUBERTY, POST-WEANING ESTRUS AND BLOOD HORMONE LEVELS OF LACOMBE GILTS

Abstract

Lacombe gilts which were exposed to a boar at 55 kg liveweight reached puberty at an average age of 145 days (range 102–200 days) and an average weight of 78.9 kg (range 55–118 kg). Restricting energy intake to 85% of free-choice intake from 45 to 90 kg increased the age at 90 kg by approximately 7 days but decreased the age at puberty by 9 days. Level of energy intake before service had no significant effect on the number of pigs born or weaned per litter. The overall average number of pigs born alive was 9.5, with 7.8 weaned per litter. Ninety-three percent of the gilts were rebred and the average time taken to post-weaning estrus was 8 days. Depriving the gilts of feed and water on the day of weaning did not significantly affect the time taken to return to estrus or influence the levels of any of the blood hormones measured. In sows that came into heat within 10 days of weaning, peak plasma concentrations of follicle stimulating hormone (FSH) occurred on the day of weaning or the 1st day after weaning, and plasma concentrations of luteinizing hormone (LH) and estradiol were low at weaning but reached peak concentrations on the day of estrus or the day prior to estrus. Patterns of plasma FSH, LH and estradiol were different in sows that failed to show an early post-weaning estrus.