Pregnancy establishment and maintenance after the administration of equine chorionic gonadotropin (eCG) associated or not with gonadotropin-releasing hormone (GnRH) after insemination in sheep

Abstract

It was recently demonstrated that equine chorionic gonadotropin (eCG) treatment 10 days after ovulation increases serum progesterone concentrations in sheep. The objective of the present study was to evaluate pregnancy outcomes induced with the administration of eCG and gonadotropin-releasing hormone (GnRH) after insemination. Three experiments were conducted in multiparous ewes that received fixed-time intrauterine insemination (Day 0) after a progesterone-based protocol for oestrus synchronisation. Experiment 1 consisted of 408 ewes, randomly assigned to three experimental groups; ewes in the first and second group received 400 IU of eCG on Day 5 and Day 10 after insemination respectively, while ewes on the third (control) group did not receive eCG. In Experiment 2, 587 ewes were randomly assigned to four experimental groups (2 × 2 factorial experiment), to receive or not 400 IU of eCG on Day 5, associated or not with 100 µg of GnRH analogue on Day 6 (i.e. 30 h after eCG administration). In Experiment 3, 715 ewes were randomly assigned to four experimental groups (2 × 2 factorial experiment), to receive or not 400 IU of eCG on Day 10, associated or not with 100 µg of GnRH analogue on Day 11 (i.e. 30 h after eCG administration). Pregnancy diagnosis was determined on Day 30 and Day 70 by ultrasonography. The eCG treatment after insemination failed to improve pregnancy outcomes in Experiments 1 and 2. However, in Experiment 3 the treatment with eCG on Day 10 enhanced pregnancy rate on Day 30, although this improvement was not maintained on Day 70, which showed greater pregnancy failure. The administration of GnRH on Day 6 or Day 11, preceded or not by eCG, did not affect any of the variables related to pregnancy. In summary, the improvement in progesterone profiles induced by eCG treatment on Day 10 after insemination, previously reported in sheep, seems to have a marginal positive effect on pregnancy establishment during the first month, which is not maintained during the second month of gestation.