Breeding gilts at natural or a hormone-induced estrus: Effects on performance over four parities

The exogenous gonadotropins— equine chorionic gonadotropin (eCG; also known as PMSG) and human chorionic gonadotropin (hCG)— can be used to stimulate the onset of estrus and ovulation in gilts and sows.1 The decision to employ exogenous gonadotropins, however, must take into account the possibility that using them to stimulate quiescent ovaries may result in the breeding of females that are otherwise innately relatively infertile. Should this occur, it is reasonable to expect longevity and lifetimepigs-produced in those females to be reduced. We recently examined a database in which primiparous sows received 400 IU eCG with 200 IU hCG (PG600®, Intervet; Whitby, Ontario) at weaning, and found no effect on lifetime productivity.2 The animals involved in that study, however, had some proven degree of fertility in that they had successfully delivered and reared a litter. Many animals are culled for infertility prior to producing their first litter.3 It is possible that relatively infertile gilts that farrow after being bred at a gonadotropin-induced estrus will have a reduced lifetime performance.