A single injection of 400 i.μ. pregnant mare's serum gonadotrophin (PMSG) plus 200 i.μ. human chorionic gonadotrophin (HCG) has been shown to induce puberty in a high proportion of gilts treated (Burnett and Walker, 198S). However, studies indicate that the hormone treatment may fail to initiate normal oestrous cycling after the pubertal ovulation. The work of Paterson and Lindsay (1981) has shown that housing gilts in contact with boars throughout the cycle after puberty induction will enhance the proportion of animals which maintain cyclic activity to a second ovulation. The purpose of the experiment reported here was to examine the effect of boar contact and the timing of the introduction of boar contact on the maintenance of cyclic activity after puberty induction by PMSG + HCG.

Puberty can be stimulated from about 160 days of age by the introduction of a mature boar usually in accomodation which is novel to the gilt. The interval between stimulation and response is not always predictable and therefore does not facilitate the synchronisation of gilt matings with the mating pattern in an established sow herd. It has been reported previously that a single injection of pregnant mares’ serum gonadotrophin (PMSG) pits human chorionic gonadotrophin (HCG)* will initiate puberty. The investigations reported here concern the use of these exogenous hormones as an additional or alternative stimulus to those described above.