Optimal timing of artificial insemination (AI) in gilt breeding programs is crucial to ensure successful fertilization and improve reproductive efficiency.  Heat detection is a key component of the effective use of AI, but is time consuming and labour intensive.  The use of hormone treatment to control the timing of ovulation can eliminate the need for heat detection and facilitates the use of fixed-time AI procedures.  Recent research has demonstrated that porcine luteinizing hormone (pLH) can reliably synchronize ovulation in weaned sows as a part of fixed time AI protocols, but its application in gilts for this purpose has not been studied.

In a study carried out at the University of Alberta, 45 cyclic gilts received altrenogest (Regumate, Intervet) treatment for 14-18 days, followed by 600 IU of equine chorionic gonadotropin (eCG), given 24 hours after the last altrenogest.  They were then treated with either 5 mg pLH, 750 IU human chorionic gonadotropin (hCG), or with saline (controls), 80 hours after the eCG treatment.

Injection with pLH or hCG will induce ovulation.

Estrus detection and ultrasound scanning was performed every 8 hours, beginning 8 hours before the pLH/hCG/saline treatment to determine the time of onset of estrus and ovulation.  The pLH and hCG treated animals were inseminated at 32 hours and, if ovulation was not yet confirmed, again at 40 hours after the pLH/hCG treatment.  Control animals were inseminated 16 hours following the initial detection of standing estrus and then every 24 hours until ovulation was confirmed. 

The results of the trial showed that the pLH and hCG treated gilts ovulated sooner after treatment compared to the control group.  Gilts treated with pLH exhibited significantly less variation in the timing of ovulation than the hCG or control groups.  Ovulation rate and number of embryos recovered was highest in the pLH treated gilts and lowest in those treated with hCG.  For gilts given pLH or hCG, the diameter of the largest follicle prior to the onset of ovulation (8.1mm and 8.1mm respectively) was smaller than control animals (8.6mm).  The pLH and hCG groups ovulated sooner after treatment compared to the saline treated group (43.2, 47.6 and 59.5 h, respectively), with significantly less variation in the timing of ovulation for the pLH-treated animals.  Embryo quality, evaluated using total cell counts and embryo diameter, was not affected by hormone treatment.

WHJ comment:  Fixed-time AI, with a single insemination, has been successfully used for sows following weaning. These results indicate that pLH can be used in cyclic gilts, and will reliably synchronize ovulation without detrimentally affecting ovulation rate, number of embryos or embryo quality.  This suggest that pLH based fixed-time AI protocols in could also be applied in gilts.

Reference:  K.L. Degenstein, R. O’Donoghue, J. Patterson, E. Beltranena, D.J. Ambrose, G.R. Foxcroft and M.K. Dyck – Synchronization of ovulation in cyclic gilts with Porcine Luteinizing Hormone (pLH),   Advances in Pork Production (2008) Volume 19, Abstract #26