GxE

Account for genotype - temperature-humidity index interactions to refine mortality traits in young calves

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Abstract

In a context where improving animal welfare and limiting the carbon footprint of livestock farming are priorities, reducing cattle mortality has become a major challenge. Calf survival is influenced by multiple interacting factors, including genetics and environmental conditions such as pathogen exposure and climatic stress. Young calves are particularly sensitive to the cold because they have limited thermogenic capacity. Cold, humid conditions are also known to affect calves' immune systems and to increase the incidence of disease. Although mortality traits generally have low heritability, previous studies have indicated the existence of genetic variability in calf survival. This study investigated the interactions between genotype and weather conditions in order to determine whether there is a genetic variability in the cold sensitivity of young Holstein calves. Phenotypic survival data from the French bovine genetic database were combined with weather meteorological records from MeteoFrance (the French meteorological agency), to link survival and death phenotypes to the weekly average temperature-humidity index (THI) during the calves' first month of life. Six mortality traits were defined according to calf age and sex: weeks 1 to 4 for females and weeks 1 to 2 for males. To exclude mortality events due to dystocia calving, the study focused on calf mortality between 2 and 30 days of age. These performance data were recorded from a total of 3,373,733 females and 2,626,387 males, born respectively from 5,926 and 6,014 sires. The pedigree of sires was traced back four generations and comprised 19,836 animals after trimming. The Interactions between genotype and weather conditions were estimated using reaction norms models that fit the genetic effects of the sires with THI-dependent second-order Legendre polynomials. Phenotypically, our study confirmed that calves are more sensitive to low THI than to high THI. At the national level, the survival rates per week dropped below 98% for females and below 97% for males during the winter months. Focusing on the mortality of 3-week-old females, heritability estimates were low across a broad range of moderate THI conditions (THI 45-70; h²=0.004), but increased substantially under cold-humid stress (THI 35; h²=0.015) as a result of rising genetic variance. Despite the overall low heritability of the trait, the genetic coefficient of variation reached approximately 50%, indicating large potential for genetic improvement. Interestingly, genetic correlations below 0.8 were observed between the mortality traits (e.g., rg=0.58 between THI35 and THI55 for 3-week-old females), demonstrating significant genotype-by-environment interactions and confirming the existence of genetic differences in cold sensitivity. These results highlight the potential for genetic selection to improve calf robustness to climatic stress, particularly in the context of increasing climate variability. We gratefully acknowledge MeteoFrance for access to the Safran database.

Keywords: 2026

How to Cite:

Leclerc, H., Venot, A. & Vinet, A., (2026) “Account for genotype - temperature-humidity index interactions to refine mortality traits in young calves”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286500. doi: https://doi.org/10.31274/wcgalp.24031

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