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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #409106
Research Project: Agroecological Approach to Enhance U.S. Sheep Industry Viability and Rangeland Ecosystem Conservation

Location: Range Sheep Production Efficiency Research

Title: Genetic impact of external Targhee sires at the U.S. Sheep Experiment Station: A case study of introgression

Author
item Wilson, Carrie - Welsh
item Taylor, Joshua - Bret
item LEWIS, RONALD - University Of Nebraska
item NOTTER, DAVID - Virginia Tech

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2024
Publication Date: 3/26/2024
Citation: Wilson, C.S., Taylor, J.B., Lewis, R.M., Notter, D.R. 2024. Genetic impact of external Targhee sires at the U.S. Sheep Experiment Station: A case study of introgression. Translational Animal Science. 8. Article txae044. https://doi.org/10.1093/tas/txae044.
DOI: https://doi.org/10.1093/tas/txae044

Interpretive Summary: Beginning in 2013, stakeholders requested that the U.S. Sheep Experiment Station (USSES) participate in national genetic evaluation through the National Sheep Improvement Program (NSIP). The reasons included the need for 1) a comparison of the productivity of industry and USDA lines, 2) transparency of USDA flocks, 3) provide genetic ties for NSIP by sampling of industry flocks, and 4) develop premium genetic lines for public release. In response, USSES began to incorporate external sires from NSIP participating flocks into the USSES Targhee flock. Between 2015 and 2017, sixteen external sires were incorporated into the flock followed by two additional sires three years later. Of the 704 offspring produced by external sires, 17 ram lambs and 132 ewe lambs were retained for breeding. By 2023, external genetics comprised almost half of the genetic makeup of the USSES Targhee flock. Stakeholder needs were met by participating in NSIP and incorporating external sires in the USSES Targhee flock.

Technical Abstract: Sheep breeders requested that the U.S. Sheep Experiment Station (USSES) participate in national genetic evaluation through the National Sheep Improvement Program (NSIP). The reasons included the need for 1) a comparison of the productivity of industry and USDA lines, 2) transparency of USDA flocks, 3) provide genetic ties for NSIP by sampling of industry flocks, and 4) develop premium genetic lines for public release. In response, USSES began to incorporate external sires from NSIP participating flocks into the USSES Targhee flock. A pedigree-based analysis of the introgression of external genetics into the flock is presented. The pedigree file included 13,189 animals with mean maximum generations, mean complete generations, and mean equivalent complete generations of 4.2, 1.8, and 2.6, respectively. The mean generation interval was 3.1 years. The reference population was defined as lambs born 2021 to 2023 (n=792). Two additional populations included the current mature ewe flock (n=123) and the current mature rams (n=14). The Genetic Conservation Index averaged 7.7 for the full population and 25.7 for the reference population. Overall inbreeding was 0.003 (0 to 0.250) for the full population and 0.006 (0 to 0.036) for the reference population. The rate of inbreeding was 0.0003 per year. Average relatedness was 0.015 (0 to 0.052) for the full population and 0.018 (0.001 to 0.026) for the reference population. The effective number of founders, effective number of ancestors, and founder genome equivalents contributing to the reference population were 60, 39, and 19.1, respectively. The ratio of the effective number of founders to the effective number of ancestors was 1.5, indicating the presence of genetic bottlenecks. Measures of effective population size ranged from 102 to 547. Of the 704 offspring produced by external sires, 17 ram lambs and 132 ewe lambs were retained for breeding. The USSES sires produced 299 offspring with 2 ram lambs and 51 ewe lambs retained. Incorporating external sires resulted in a cumulative percentage of genetic variance of 48.8, 49.1, and 44.2 of external genetics for the reference population, current mature ewe flock, and current mature rams, respectively. Stakeholder needs were addressed by introgression of external sires and participation in NSIP, but future selection practices need to be modified to maintain a minimum of 50 percent USSES core genetics in the flock.