Critical factors for non-surgical artificial insemination in sheep

Abstract

USDA National Animal Germplasm Program is responsible for collecting germplasm from agriculturally relevant species in the US and developing methods for its efficient and effective storage and utilization. Lack of low cost and effective use of assisted reproductive technologies in sheep has been problematic and impacts the effective use of germplasm. While ram semen can be cryopreserved, methods for its use via non-surgical artificial insemination (AI) are not well developed. Consequently, we performed multiple trials to identify methods that result in ewe fertility when using cryopreserved ram semen, synchronized estrous, and timed non-surgical AI to identify factors that influence fertility. Experiment 1 used Black Welsh Mountain sheep and resulted in 51 % of bred ewes lambing. Statistical analysis showed age of the ewe, ram, and interaction of ewe age X time of AI effects were not significant. However, AI time relative to CDIR removal impacted fertility (P < 0.001). In a second experiment using Rambouillet, 11 % of artificially inseminated ewes lambed. A statistical model that included the effects of AI time, ewe age, and the AI time X ewe age interaction was not significant (P > 0.05). Experiment 3 utilized both breeds of sheep and resulted in mean fertility of 48 and 13 % for Black Welsh Mountain and Rambouillet, respectively. Analysis of the fertility results in experiment 3 included the effects of ewe breed, time of AI, ram, and the 2 and 3-way interaction terms. The three-way interaction of ewe breed X ewe age class X AI time was significant (P < 0.001) as were all two way interactions (P < 0.05). Identification of this 3-way interaction indicates that AI methodology is complicated and requires tailoring to specific breeds, ewe ages classes, and AI timing. These results suggest, at least partially, reasoning for highly inconsistent results reported in previous literature and the difficulty in applying the technology in the field. Potential approaches to address these important interactions in search of a more predictable result are discussed.