GxE

Genotype-by-environment interaction for methane emissions in Holstein cows under heat stress conditions

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Abstract

Enteric methane emissions from dairy cattle represent a source of greenhouse gases, underscoring the importance of mitigating them to achieve sustainable livestock systems. Heat stress (HS) alters key physiological and metabolic functions in lactating cows, leading to reduced feed intake, decreased milk production, compromised reproductive efficiency, and heightened susceptibility to health disorders. Additionally, HS may also modulate methane production per animal, thereby affecting total methane emission outputs. Gaining insight into genotype-by-environment interactions (Gà—E) under HS conditions is crucial for developing resilient breeding strategies that preserve their effectiveness as elevated temperatures become increasingly prevalent due to climate change. This study aimed to estimate genetic parameters for methane production across a Temperature-Humidity Index (THI) gradient and to evaluate sire re-ranking to quantify Gà—E effects under HS. Weekly averages of methane production (MetP, g/day) were computed from 9,923 Holstein cows across five U.S. commercial herds. Weather data were retrieved from the NASA POWER database and used to calculate daily THI. To align environmental and production records, daily THI values were aggregated into weekly averages matching the methane production intervals. A single-trait reaction norm linear model that assumed the negative impact of HS occurred at THI >70 was implemented to estimate the heritability of methane across THI values and to obtain genomically estimated breeding values (gEBV) under varying HS conditions. The evaluation was conducted using the single-step genomic BLUP (ssGBLUP) methodology. Fixed effects included in the model were lactation (1 to 4+) combined with lactation stage (before and after peak), age‑at‑calving class, and herd‑year of calving. As individual feed intake and weight records were unavailable for all animals, size differences were indirectly accounted for through lactation grouping. Random effects included additive genetic effect, random regression on THI for HS genetic effect, permanent environment, and random regression on THI for the permanent environment. Based on gEBV at THI ≤70 (thermoneutral conditions), genotyped bulls with ≥100 progenies were classified as High (n=100) or Low (n=100) methane emitters to assess their response under HS. Heritability of MetP increased from 0.27 at THI 70 to 0.47 at THI 85, indicating a considerable influence of HS over the genetic potential of animals for methane emissions. Sire's gEBVs showed marked re-ranking across the THI gradient. Under thermoneutral conditions, high-emitting sires showed positive gEBV, whereas low-emitting sires were negative. Beyond THI 77, trajectories intersected: gEBV for high emitters declined, while those for low emitters increased. This crossover pattern demonstrates strong Gà—E, indicating that selection based only on thermoneutral performance may not ensure optimal outcomes under HS. The increased heritability and pronounced sire re-ranking under HS reinforce the need to account for Gà—E in methane mitigation strategies. Breeding programs should incorporate multi-environment evaluations to maintain selection accuracy when HS occurs.

Keywords: 2026

How to Cite:

Gonzalez-Peña, D., Sánchez-Castro, M., Oliveira, G., Pacheco, H., Vargas, G., Kulkarni, A. & Vukasinovic, N., (2026) “Genotype-by-environment interaction for methane emissions in Holstein cows under heat stress conditions”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285835. doi: https://doi.org/10.31274/wcgalp.23805

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