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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #430259
Research Project: Discovery of Novel Traits to Improve Efficiency and Sustainability of Different Sheep Production Systems

Location: Livestock Bio-Systems

Title: The U.S. National Sheep Improvement Program: Historical insights and emerging frontiers

Author
item Murphy Jr, Thomas
item BRITO, LUIZ - Purdue University
item HESS, ANDREW - University Of Nevada
item BROWN, DANIEL - University Of New England
item LEWIS, RONALD - University Of Nebraska
item NOTTER, DAVID - Virginia Tech

Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Abstract Only
Publication Acceptance Date: 5/8/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The National Sheep Improvement Program (NSIP) began in 1987 and remains the only comprehensive across-flock genetic evaluation system for the U.S. sheep industry. Underlying methodologies have continued to evolve, but at its core the NSIP generates estimated breeding values (EBV) for use in selection by commercially oriented seedstock breeders across the country. Our aims were to provide estimates of inbreeding and genetic trends within five U.S. sheep breeds. The predominant terminal sire (Suffolk), fine-wool (Rambouillet and Targhee), maternal wool (Polypay), and maternal hair (Katahdin) breeds in the NSIP were chosen for analyses. Pedigree- (all breeds) and/or genomic-based (Katahdin only) EBV and inbreeding coefficients were extracted from the October 2025 NSIP report. Traits included: direct and maternal components of weaning weight (WWT and MWWT, respectively); post-weaning weight (PWWT), ultrasound loin muscle depth (PEMD), and fecal egg count (PFEC, Katahdin only); number of lambs born per ewe lambing (NLB); and yearling greasy fleece weight (YGFW) and fiber diameter (YFD; Rambouillet and Targhee only). Genetic trends were estimated after averaging EBV within birth year (2010 – 2024) and regressing annual mean EBV on year of birth for all individuals whose EBV accuracy exceeded trait-specific reporting thresholds. Inbreeding trends were estimated in a similar manner. The total number of individuals and flocks, respectively, with WWT EBV was: Suffolk (19,814 and 35), Rambouillet (29,586 and 23), Targhee (33,182 and 42), Polypay (68,243 and 73), and Katahdin (86,869 and 153). Trends for WWT and PWWT were significant in all breeds (P < 0.001) and numerically greatest in Suffolk (0.17 and 0.30 kg/yr, respectively) followed by Katahdin (0.09 and 0.15 kg/yr), Polypay (0.05 and 0.11 kg/yr), Targhee (0.05 and 0.09 kg/yr), and Rambouillet (0.03 and 0.06 kg/yr). On average, MWWT increased (P < 0.001) in Polypay (0.06 kg/yr), Targhee (0.05 kg/yr), and Katahdin (0.03 kg/yr) but not in Suffolk or Rambouillet. A trend in PEMD was only observed in Rambouillet and Targhee (0.03 mm/yr; P < 0.001). All breeds had a positive NLB trend (P < 0.01), being numerically greatest in Polypay (0.005 lambs/yr) and lowest in Suffolk and Rambouillet (0.002 lambs/yr). While YGFW increased (P