Of all sows weaned, 95% returned to estrus within 10 days. All PE2 sows exhibited a second postweaning estrus at an average of 22 days after their first postweaning estrus (range 19.1 to 28.4 days). All PE1 sows and 96% of PE2 sows were bred. There were no differences between PE1 and PE2 sows for pregnancy rates, which exceeded 90%.

Although there was no difference in ovulation rates between treatments, PE2 sows had greater numbers of live embryos and higher embryonic survival at Day 30 of gestation compared to PE1 sows (Table 3).

These results confirm that under good management practices, high production performance is achievable.

The study confirms that breeding first-parity weaned sows at second postweaning estrus will negate the effects of the second-parity dip. Consistent with a previous study, 22 NPDs were accumulated and an additional 2.3 live embryos at Day 30 were detected. However, in this study, all “skipped” sows were detected in heat and were successfully bred.

Current expectations are that one additional pig born/litter will cover the additional cost of 21 NPDs ($2/day × 21 days = $42). If the use of this management practice increases the number of pigs born by more than one, a positive cost:benefit ratio would be anticipated.

Alternative methods to increase second-parity litter size, without the accumulation of the NPDs associated with skip-a-heat breeding, merits further investigation.

Researchers: J.L. Patterson, P.R. Zimmerman, M.K. Dyck and George R. Foxcroft, University of Alberta, Edmonton, Alberta, Canada. Contact Foxcroft by phone (780) 492-7661 or e-mail: george.foxcroft@ualberta.ca.