Timing of insemination relative to ovulation in pigs: Effects on sex ratio of offspring

Abstract

The objective of the present study was to identify effects of the interval between insemination and ovulation in pigs on the sex ratio and sex ratio dispersion of offspring. Crossbred sows that had farrowed 2 to 9 litters were weaned (Day 0) and came into estrus between Days 3 and 7 after weaning. Ultrasonography was performed every 6 h, from 12 h after the onset of estrus until ovulation had been observed. The sows were inseminated once at various intervals from the onset of estrus. At farrowing, the numbers of viable piglets and dead piglets were recorded per sow. In four 12-h intervals between insemination and ovulation (36 to 24 h before ovulation, 24 to 12 h before ovulation, 12 to 0 h before ovulation and 0 to 12 h after ovulation), the total number of piglets was (mean±SEM)10.8 ± 1.2 (n = 15); 13.4 ± 0.7 (n = 23); 13.2 ± 0.9 (n = 21); and 12.1 ± 1.0 (n=16), respectively (P>0.05). The percentage of male piglets per litter in the four 12-h intervals was 52.1 ± 3.6, 50.5 ± 2.7, 54.9 ± 2.8 and 47.8 ± 4.5, respectively (P>0.05). Sex ratio was not influenced by litter size (P>0.05), and its distribution was normally dispersed (i.e., as expected under a binomial distribution) in all 4 intervals between insemination and ovulation (P>0.05).