Effect Of Semen Dose On Pregnancy Rate Using Liquid Semen Ai In Hair Sheep

Two experiment were conducted in November, using land race hair sheep ewes (n=44) on-site (Exp 1), and grade Katahdin ewes (Exp 2) off-site, to evaluate the effect of semen dose on AI pregnancy rates. Estrus was synchronized by inserting CIDR devices for 12 d. For AI, ewes were assigned balanced by age to three groups, and inseminated twice with either 75, 150, or 225 million sperm twice at 48 and 54 h after CIDR removal by vaginal AI. Semen was collected on the day of insemination from landrace hair sheep rams (Exp 1: n=6; Exp 2: n=10) by artificial vagina, and ejaculates pooled. Subsamples of the pooled ejaculate were extended in a UHT skim milk and egg yolk (5% v/v) extender to final concentrations of 150, 300, and 450 million sperm/ml, and packaged in 0.5 ml straw. Semen was held at 36°C during processing (2–3 h). In Exp 1 the first insemination was carried out immediately after processing, and the second with semen stored at 5°C. In Exp 2 semen was transported (3 h) and stored at 5°C prior to inseminations. Pregnancy to AI was determined by transrectal ultrasonography. Semen quality differences were analyzed using PROC GLM and pregnancy rate differences using PROC FREQ in SAS. Sperm motility (94.2 vs. 68.0%) and concentration (5.84 vs. 6.62 billion sperm/ml) were higher (P<0.001) in ejaculates contributing to the pool in Exp 1 than Exp 2. Pregnancy rates were 21.4, 46.6, and 40.0% in Exp 1 (P=0.35) and 22.7, 15.8, and 25.0% in Exp 2 (P=0.77) for doses of 75, 150 and 225 million sperm, respectively. In conclusion, improved conditions (higher sperm motility and shortened storage time) tended to increase pregnancy rates when ewes were inseminated with higher concentrations of semen.