Gonadotropin stimulation using P.G. 600® on reproductive success of non-lactating anestrous ewes

Abstract

The effect of stimulation with a gonadotropin preparation with combined follicle stimulating and luteininzing hormone like activity on reproductive success in anestrous ewes was evaluated. In Experiment 1, ewes of mixed breeding were treated with CIDR inserts (0.3g progesterone) for 5 days and were assigned randomly to receive either gonadotropin stimulation (3mL i.m. injection of P.G. 600®, 240IU eCG and 120IU hCG) at CIDR removal or no further treatment. Intact raddled rams were joined at insert removal for 30–35 days, and ewes were observed for indications of estrus after 4 days of ram exposure. Pregnancy diagnosis was conducted via transrectal ultrasonography at the time of ram removal and again 20–25 days. The second experiment was similar to Experiment 1, except treated ewes received the gonadotropin 1 day prior to insert removal. In Experiment 1, incidence of estrus was greater for treated ewes (P=0.01), and prolificacy tended to be greater in treated ewes (P=0.06). In Experiment 2, treated ewes had greater conception rates (P=0.01), pregnancy rates to first service (P=0.0007), and tended to have greater overall pregnancy rates than control ewes (P=0.07). A greater percentage of ewes lambed in the gonadotropin treated ewes than in ewes in the control group (P<0.0001), and overall lambing rates in treated ewes were greater than non-treated controls (P<0.0001). In conclusion, gonadotropin treatment 1 day prior to CIDR removal increased reproductive success in progesterone-treated anestrous ewes.