Effect of progestagens and eCG with GnRH on lambing rates

摘要

The effect of progestagens Spong or CIDR and eCG with GnRH injections on lambing rate was evaluated. Anestrous ewes (83) pre-treated In Situ with intravaginal progestagen sponges or CIDR for 14 days and Pregnant Mare Serum Gonadotrophin (upon removalof sponges or CIDR), were used. Two days after removal of the sponges or CIDR, ewes were injected IM with distilled water (sponge or CIDR, control group), or GnRH analogue (sponge or CIDR, GnRH group). Lambing rates of ewes following induced first oestrus was 86.7% in CIDR, 58.3 % in sponge, 66.7% in sponge GnRH and 55% in CIDR GnRH. Twin lamb birth rate was 57.1% higher in sponge controls compared with CIDR and GnRH groups. Litter size was higher in sponge controls compared with CIDR control and GnRH groups. These results suggest that GnRH injection 2 days after sponge or CIDR removal, does not increase lambing rates of anoestrous ewes. However, further studies are needed to evaluate the effect of GnRH on the lambing rate outside the breeding season.