Benchmarking performance in Targhee sheep in development of a genetic reference flock

Authors: Wilson, Carrie; Taylor, Joshua; NOTTER, DAVID - Virginia Tech; Murphy Jr, Thomas; STEWART, WHITNEY - University Of Wyoming; LEWIS, RONALD - University Of Nebraska

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2024
Publication Date: 12/17/2024
Citation: Wilson, C.S., Taylor, J.B., Notter, D.R., Murphy, Jr., T.W., Stewart, W.C., Lewis, R.M. 2024. Benchmarking performance in Targhee sheep in development of a genetic reference flock. Translational Animal Science. 8. Article txae176. https://doi.org/10.1093/tas/txae176.
DOI: https://doi.org/10.1093/tas/txae176

Interpretive Summary: The objective of this research was to incorporate external sires participating in national genetic evaluation through the National Sheep Improvement Program (NSIP) into the U.S. Sheep Experiment Station (USSES) flock to compare sire performance and obtain genetic parameter estimates for production traits. The USSES is one of three USDA, ARS units that have sheep flocks; these units are in the process of establishing genetic reference flocks (GRF) to serve sheep producers through incorporation of industry sires into the research flocks, exchange of genetics among ARS flocks, and creating opportunity to study genetics by environment by management interactions. Sixteen rams, representative of sires used in commercial flocks, were purchased from 10 NSIP Targhee flocks. The progeny performance of the external sires and 12 USSES sires was compared by evaluating their NSIP estimated breeding values, the performance of their progeny from 2016 to 2018, and the performance of their progeny and other descendants that were retained in the flock from 2016 through 2022. External sire and USSES sire performance differed for one NSIP trait, the NSIP Western Range Index, and three fleece traits. Establishment of a Targhee GRF at USSES has been initiated and can now be used to accomplish industry goals.

Technical Abstract: The Targhee breed is important to range sheep production in the Western U.S. The objective of this research was to integrate external sires participating in national genetic evaluation through the National Sheep Improvement Program (NSIP) into the U.S. Sheep Experiment Station (USSES) flock, where the breed originated, to benchmark sire performance and obtain genetic parameter estimates for production traits. Estimated breeding values (EBV) of external sires (n = 16) and USSES sires (n = 12) from the 2023 NSIP Targhee genetic evaluation differed (P < 0.05) only for the NSIP EBV for number born. This difference, and small (nonsignificant) differences favoring external sires for maternal weaning weight, yearling fiber diameter, and yearling staple length EBV also resulted in greater (P < 0.05) Western Range Index scores for external sires. The performance of sires’ direct progeny born 2016 to 2018 was compared for 17 traits. After data cleaning, there were 664 progeny (417 from external sires and 247 from USSES sires) with 146 to 664 records per trait. Least squares means differed (P < 0.05) for grease fleece weight, side fiber diameter, and britch fiber diameter in favor of the external sires. Production traits were measured from the progeny and other retained descendants of both sire genetic groups from 2016 through 2022. After data cleaning, there was a range of 1,138 to 1,493 records per trait. A three-generation pedigree was constructed and the proportional assignment of each lamb to each genetic group was included in an augmented relationship matrix. A univariate animal model was fitted for each lamb trait and a repeated measures model for each of three ewe traits was fitted to estimate variance components and predict breeding values. Heritability (h2) estimates for lamb production traits were 0.23, 0.34, 0.43, 0.39, and 0.31 for direct birth weight, maternal birth weight, average daily gain to 120 d, 120-d weight, and the binary trait of lamb survivability, respectively. Total litter weight to 120 d had a h2 of 0.06 and a repeatability (r) of 0.17. Number of lambs born and number of lambs weaned were analyzed as ordinal traits with h2 estimates of 0.02 and 0.04, respectively, and r estimates of 0.10 and 0.18, respectively. Genetic group solutions did not differ (P > 0.05) for any of these traits. Establishment of a Targhee genetic reference flock at USSES has been initiated, which can be used to address issues of importance to the industry.