Effect of equine chorionic gonadotropin on weaning-to-first service interval and litter size of female swine

We evaluated the effect of PMSG on the weaning-to-first service interval, t otal litter size and born alive litter size in swine. Four doses of PMSG (0 , 500, 750 and 1,000 IU) were administered intramuscularly after weaning to sows at 3 different farms, grouped by parities (1, 2 and 3 or higher) and 2 distinct time periods. The associations among main effects and response v ariables were assessed by analysis of variance. Polynomial orthogonal terms were used to adjust the estimates of weaning-to-first service interval, to tal litter size and born alive litter size for the interaction effect of pa rity and PMSG treatment. The weaning-to-first service interval did not diff er across periods and farms (P>0.05), although the interval was shorter (P< 0.05) for Parity 3+ sows (4.97 d) than for Parity 1 sows (5.29 d), with no Other differences in intervals observed across parities (P>0.05). Time peri od did not influence litter size (P>0.05), but there were differences in li tter size across farms (P<0.05). Both litter size traits were lower for Par ity 1 sows than for higher parity sows (P<0.05), but there were no differen ces in litter size between Parity 2 and 3+ sows (P>0.05). Litter size incre ased with PMSG dose in both Parities 1 and 2 (P<0.05), but not in Parity 3 (P>0.05), A significant quadratic effect (P<0.05) of PMSG treatment in wea ning-to-first service interval was observed for both Parity 1 and 2 sows, w ith the shortest intervals occurring with the 750 IU dose for Parity 1 sows . Administration of PMSG after weaning was associated with a shortened wean ing-to-first service interval in Parity 1 sows and increased litter size in Parity 1 and 2 sows. (C) 1999 by Elsevier Science Inc.