Genetic parameter estimates for lamb survivability as separate traits based on birth type for Polypay, Rambouillet, Targhee, and Suffolk sheep

Authors: Wilson, Carrie; Taylor, Joshua

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2026
Publication Date: 7/27/2026
Citation: Wilson, C.S., Taylor, J.B. 2026. Genetic parameter estimates for lamb survivability as separate traits based on birth type for Polypay, Rambouillet, Targhee, and Suffolk sheep. Journal of Animal Science. 104. Article skag217. https://doi.org/10.1093/jas/skag217.
DOI: https://doi.org/10.1093/jas/skag217

Interpretive Summary: Lamb survivability is of economic importance to sheep producers due to its role in reproductive efficiency. A comprehensive threshold model analysis was undertaken to determine the most appropriate lamb survivability model for each of four sheep breeds at the U.S. Sheep Experiment Station. The breeds included the Polypay, Rambouillet, Targhee, and Suffolk and included records from 1980 to 2024. In addition to determining the most appropriate model for each breed, analyses included a combined data set and separate data sets by birth type. In agreement with literature estimates, both the direct and maternal components of lamb survivability were generally low. Because the direct and maternal influences differed by birth type, analyzing lamb survivability as separate traits by birth type is warranted. There were sires that had above average estimated breeding values for both direct and maternal lamb survivability, suggesting genetic progress can be made for both components of the trait.

Technical Abstract: Lamb survivability is a primary determinant of profitability in sheep production. Most published heritability estimates for this complex trait are low (< 0.05). A comprehensive analysis of lamb survivability using five random effects models of increasing complexity and three fixed effects models for combined and separate birth types for Polypay, Rambouillet, Targhee, and Suffolk U.S. sheep breeds was performed using a threshold model. Records from 1980 to 2024 from the U.S. Sheep Experiment Station were used and included 22,284 Polypay, 25,085 Rambouillet, 20,439 Targhee, and 3,965 Suffolk lamb survivability observations. For the final models for all breeds, direct heritability for at least one birth type was higher than the combined direct heritability. When the total maternal contribution was considered as maternal heritability plus the permanent environment, total maternal was higher than the direct heritability for all traits except Rambouillet and Targhee triplets. Direct heritability for the combined data set ranged from 0.013 to 0.071 and maternal heritability ranged from 0.013 to 0.038. Single direct heritability estimates ranged from 0.014 to 0.114 and maternal heritability ranged from 0.030 to 0.101. Twin direct heritability estimates ranged from 0.015 to 0.076 and maternal heritability ranged from 0.011 to 0.054. Triplet direct heritability estimates ranged from 0.010 to 0.509 and maternal heritability ranged from 0.010 to 0.354. Estimated breeding values (EBV) were computed for all pedigree animals and converted to the 80% probability scale and genetic trends were derived. Theoretical accuracies were compared. There were sires that had above average EBV for both direct and maternal lamb survivability, suggesting genetic progress can be made for both components of the trait. Correlations among current sires for single, twin, and triplet lamb survivability EBV were low and, in some cases, negative. Accuracies were generally lower when evaluating lamb survivability as separate traits by birth type; however, evaluating single, twin, and triplet lamb survivability as separate traits is warranted because the direct and maternal influences differ by birth type.