Swine

Genetics of heat tolerance in purebred maternal pig lines based on reaction norm models for reproductive performance traits

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Abstract

Sow fertility and reproduction traits are known to be negatively influenced by heat stress conditions. Then, breeding more heat tolerant pigs with improved reproductive performance is of great relevance to the pig industry. Reaction norm models provide a framework to quantify genetic differences in sensitivity to continuous environmental gradients. Therefore, this study aimed to evaluate genotype-by-environment interactions (Gà—E) for farrowing traits in Landrace (LR) and Large White (LW) populations considering the Temperature-Humidity Index (THI) as the environmental gradient. Phenotypic records were obtained from up to seven farrowing events of 31,132 LR and 24,329 LW sows across four farms. The traits evaluated included number of piglets born alive (NBA), stillborn piglets (SB), mummified piglets (NM), litter birth weight (LBW), and average piglet birth weight (APBW). The environmental descriptor was defined as the mean of the daily maximum THI over 15 days preceding farrowing, computed from NASA POWER meteorological data. Single-trait reaction norm models were fitted for each trait using Legendre orthogonal polynomials to model random additive genetic and permanent environmental effects. Estimates of additive genetic variance for farrowing traits in both lines were affected by climatic conditions, reflecting in variation of heritability along the THI gradient. Additive genetic variance generally declined with increasing THI for NBA, SB, and LBW, whereas phenotypic variance remained comparatively stable across the gradient in both lines. For NM, genetic variance increased slightly at higher THI, while APBW showed a convex pattern with increasing additive genetic variance, particularly in LR. For NBA, heritability estimates ranged from 0.11 to 0.13 in LW and 0.12 to 0.13 in LR, whereas SB ranged from 0.12 to 0.14 in both lines. LBW showed moderate environmental sensitivity, with heritability estimates ranging from 0.16 to 0.22 in LW and 0.18 to 0.23 in LR, with the highest values under low to intermediate THI (-18 to 4). NM presented low heritability (0.03 to 0.05 in both lines), with slightly increasing estimates at higher THI (5 to 27), suggesting that genetic differences become more evident under heat stress. APBW exhibited the highest heritability estimates among the traits evaluated, ranging from 0.31 to 0.34 in LW and 0.31 to 0.39 in LR. Genetic correlations across the THI gradient indicated high stability for most traits, with some line-specific environmental sensitivity. In LR, correlations between low and high THI were 0.85 (NBA), 0.78 (SB), 0.87 (LBW), 0.89 (APBW), and 0.47 (NM), whereas LW sows showed comparable values of 0.87 (NBA), 0.82 (SB), 0.82 (LBW), 0.91 (APBW), and 0.42 (NM). These patterns suggest lower Gà—E for NBA, SB, LBW, and APBW in these purebred populations, but meaningful Gà—E for NM and a greater potential for re-ranking of genetic merit under hotter conditions.

Keywords: 2026

How to Cite:

Freitas, F., Mello Cesar, A., Silva Neto, J., de Oliveira, L., Ferreira Benfica, L., Rojas-Medina, S., Bhatnagar, A., Chen, C., Holl, J., Johnson, J. & Brito, L., (2026) “Genetics of heat tolerance in purebred maternal pig lines based on reaction norm models for reproductive performance traits”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2295661. doi: https://doi.org/10.31274/wcgalp.24356

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