Effect of PG600 and adjusted mating times on reproductive performance in weaned sows

The administration of PG600 to sows at weaning induces >90% of sows to return to estrus within a week, but farrowing rate and litter size are often not improved. This study evaluated the effects of adjusted artificial insemination (AI) times based on weaning to estrus interval (WEI) and estrus to ovulation interval (EOI) following PG600. All sows were given PG600 at weaning and allotted to adjusted (ADJ, n = 47) or non-adjusted (NA, n = 46) mating times after the onset of estrus. Adjusted mating involved: (1) 2-3 days WEI, AI at 36 h and 48 h; (2) 4 days WEI, AI at 24 h and 36 h; (3) 5 days WEI, AI at 12 h and 24 h; and (4) 6-7 days WEI, AI at 0 h and 12 h. Mating for NA occurred at 0 h and 24 h after onset of estrus. There was no effect of treatment on return to estrus (92.9% versus 92.5%) or ovulation (92.7% versus 92.5% for ADJ and NA, respectively). The proportion of first AI occurring within 24 h prior to ovulation was increased (83.8% versus 50.0%) and closer to ovulation for ADJ compared to NA treatment (19.4 h versus 27.3 h, P < 0.05). Treatment did not influence (P > 0.10) the proportion of second AI occurring within 24 h of ovulation (72.8% versus 56.6%) but did influence (P < 0.05) the interval from second AI to ovulation for ADJ compared to NA (10.6 h versus 3.3 h). The ADJ treatment increased (P < 0.05) the proportion of sows that received an AI within 24 h before ovulation (98.8% versus 87.0%). However, treatment did not influence pregnancy (87.4%) or farrowing (79.5%) rates but the NA treatment tended to increase (P < 0.10) total number of pigs born (11.8 versus 8.9). In conclusion, while AI times for ADJ appeared to occur within optimal periods, farrowing rates were not improved and litter size decreased, suggesting that two AI at 12 h intervals and closer to the time of ovulation may be detrimental. Overall, these data suggest that for sows injected with PG600 at weaning and receiving two AI, breeding at 0 h and 24 h after onset of estrus is recommended.