103 Use of Liquid Semen Artificial Insemination in Katahdin Sheep in a Commercial Farm Setting.

Liquid semen vaginal artificial insemination (AI) with short-term stored semen provides a low-cost approach for moving germplasm between hair sheep flocks. Here we evaluated simulated shipping (12 h) of chilled liquid semen on pregnancy rate of purebred Katahdin ewes in an on-farm environment. Ewes in a purebred Katahdin flock (n = 100) managed under an annual breeding cycle were estrus synchronized by inserting CIDR devices for 12 d. Implants were removed 48 h before initial AI. For AI, ewes were allocated to be bred to one of five 5 to 9 mo-old Katahdin ram lambs using semen collected and processed within 2 h of AI or after storage for 12 h at 5°C in a portable refrigerator. Balanced by sire and storage time, ewes were inseminated either once by simple vaginal timed AI at 48 h after CIDR removal, or again 6 h after initial AI with semen from the same collection. Semen was collected and processed on site using an artificial vagina, extended to 250 million sperm/ml in a simple UHT skim milk and egg yolk (5% v/v) extender, and packaged into 0.5 mL straws. Ewes were exposed to natural mating 11 d after AI to the same sire used for AI. Pregnancy was determined by transrectal ultrasonography 41 d after AI. Data were analyzed by Chi-square for the effect of storage time, insemination frequency, ram, and ewe age. Sperm motility in straws at the end of the second AI session (27 h of storage) ranged from 60 to 80% in individual rams. Pregnancy rate to AI (14.1%) was lower than anticipated, but tended to be higher (P = 0.09) in fresh compared to 12 h stored semen (20.0 vs. 8.1%). Similarly, pregnancy rate tended to be higher (P = 0.09) following a double than a single insemination (20.9 vs. 8.9%). There was no effect (p = 0.88) of ram on AI pregnancy rate. Ewe age tended to effect (P = 0.09) pregnancy rates, being highest in 2 yr (30.8%), 3 yr (18.2%) and 4 yr old (18.2%) ewes, while no pregnancies were observed in ewes older than 4 yr. In contrast, pregnancy rate after clean-up mating was not affected by ewe age. Fetal numbers were no different in pregnancies resulting from AI or clean-up matings (64.3 and 71.6% multiples, respectively). Results confirm our earlier observations that insemination frequency, ewe age and storage time greatly impact the outcome of liquid semen AI.