Time of ovulation and reproductive performance over three parities after treatment of primiparous sows with PG600.

Primiparous sows from a commercial pig farm in central Brazil were utilized to investigate the effect of post-weaning gonadotrophins (given during summer) on estrus, time of ovulation and reproductive performance over three parities. One group of sows (PG600) was treated with a combination of 400 IU equine chorionic gonadotrophin (eCG)+200 IU human chorionic gonadotrophin (hCG) (PG600) 24h after weaning (n=420), whereas the control group received saline (n=408). In a subset of sows (n=150), estrus was detected and time of ovulation was determined by transcutaneous ultrasound. Treatment with PG600 increased the percentage of primiparous sows in estrus within 10 days after weaning (94.8% versus 79.7%) and reduced the first weaning-to-estrus interval (5.3 days versus 8.0 days) relative to control sows (P<0.05). Although the duration of estrus was longer (P<0.05) in sows given PG600 (65.7 h versus 61.0 h), the interval from estrus to ovulation was not different (P>0.05) between PG600 and control sows (46.6 h versus 43.3 h). Treatment with PG600 did not affect (P>0.05) rates of return-to-estrus and farrowing over three parities, but it increased the number of total piglets born (P<0.05) in the second parity (11.2 versus 10.4), thereby minimizing the magnitude of second-litter syndrome. Culling rates from the first to the fourth parity were 26.7 and 24.5% (P>0.05) for PG600 and control sows, respectively. In conclusion, PG600 given 24 h after the first weaning reduced the weaning-to-estrus interval and increased the size of the second litter.