Embryo mortality is a major cause of reproductive loss in all the farm species (Bolet, 1986). Losses of a total litter by embryo mortality account for about 15% of all services but may be substantially higher in the summer months, particularly in outdoor systems (Love et al., 1993). There has been interest in the use of gonadotrophin releasing hormone (GnRH) in cows and sheep, both on the day of service and 12 days after, to improve pregnancy rates (see review by Peters 1996) with 10 -12% improvements being reported. The mechanisms of maternal recognition of pregnancy are different between pigs and ruminants, however, a pilot study was carried out to determine whether GnRH might have similar effects in the pig.