GxE

Climate and management jointly influence the expression of weaning weight in Katahdin sheep

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Abstract

Sheep production in the U.S. occurs across diverse geographies and management systems. Katahdin, a maternal hair breed, reflects that reality. Our aims were: i) to characterize production environments in Katahdin flocks using climate and management information; and ii) to use those descriptions to test genotype-by-environment interactions (GxE) for weaning weight. A management survey was completed by 46 Katahdin flocks enrolled in the National Sheep Improvement Program. It considered gastrointestinal parasite control, lambing and udder-health management, culling strategies, feeding methods, and climate-mitigation practices. Climatic variables, including elevation, seasonal precipitation, soil moisture, and the Comprehensive Climate Index (CCI), were obtained from NASA POWER using each flock's geographic location; CCI summarized weather factors affecting animal performance. Climate and management data were integrated using multivariate methods, specifically factorial analysis of mixed data refined with linear discriminant analysis. Three environmental clusters (EC) were formed consisting of 16 (EC1), 29 (EC2), and 1 (EC3) Katahdin flocks. The clusters identified collections of flocks with different seasonal temperatures and precipitation, parasite challenges, and culling strategies. Weaning weights on 41,241 lambs, preadjusted to a 60-day recording age, were separated into three traits depending on the flock's assignment to a cluster. Amongst 1,114 sires with progeny weights recorded, 25 had offspring in both EC1 and EC2, while 6 had offspring in both EC1 and EC3. No sires were shared between EC2 and EC3. The pedigree contained 140,691 individuals. Variances were estimated within clusters with a univariate animal model using ASReml software. Fixed effects were contemporary group (concatenation of flock, birth year, lambing season, and recording date), sex, and birth-rearing type, with dam age as a continuous covariate (linear and quadratic terms). Random effects were direct and maternal additive genetic, maternal permanent environment, and residual. Estimated breeding values (EBV) were predicted. A bivariate model was also fitted to estimate the direct additive genetic covariance between clusters. For the 25 rams siring offspring in both EC1 and EC2, EBV rankings were compared with Spearman's rank correlation. Within clusters (EC1, EC2, and E3), direct heritability estimates were 0.23±0.04, 0.11±0.01, and 0.13±0.07; corresponding maternal heritability estimates were 0.04±0.03, 0.09±0.01, and 0.15±0.04; phenotypic variances were 12.52±0.32, 12.42±0.12, and 19.36±0.99 kg2. Environmental differences amongst clusters seemingly underpinned the observed heteroscedasticity in genetic and phenotypic variances. For pairs of clusters with shared sires, genetic correlations were 0.78±0.22 (EC1:EC2) and 0.30±0.73 (EC1:EC3). Spearman rank correlations were 0.22 (p = 0.29) for sires with progeny in EC1 and EC2. Although a limited number of sires was shared across those clusters, their substantial reranking inferred GxE for weaning weight. That conclusion was substantiated by the moderate genetic correlation between weights recorded in EC1 and EC3. Accounting for such factors in genetic evaluation programs may improve the robustness of selection decisions.

Keywords: 2026

How to Cite:

Yazar Gunes, H., Howard, R., Murphy, T., Freking, B., Wilson, C., Burke, J., Taylor, B., Brito, L. & Lewis, R., (2026) “Climate and management jointly influence the expression of weaning weight in Katahdin sheep”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2284784. doi: https://doi.org/10.31274/wcgalp.23616

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