Genetic relationships among methane emissions from breath, dry matter intake, body weight, and milk production traits of Dutch dairy cows

Reducing enteric methane (CH₄) emissions from dairy cattle is essential to mitigate the environmental footprint of dairy farming. This study aimed to investigate genetic correlations between CH₄ emissions and key production traits in Dutch dairy cows. Methane concentrations (CH₄c) and CO₂ concentrations were measured using nondispersive infrared sensors, called sniffers, that sampled from the feed bin of automatic milking systems. Data on CH₄ were collected on 7,139 cows from 68 commercial farms in the Netherlands between 2019 and 2023. On an additional set of experimental farms, phenotypic data on milk production traits, BW, and DMI were recorded on 9,550, 7,049, and 7,546 cows, respectively. Genetic parameters were estimated with bivariate models for cows in their first, second, and third or greater parity separately using ASReml v4.2.1. The heritability for weekly averages for CH₄c ranged from 0.21 to 0.27, whereas the repeatability ranged from 0.65 to 0.73 across different parities. Genetic correlations between CH₄c and DMI were weak and positive, ranging from 0.06 to 0.15 across parities. Similarly, genetic correlations between CH₄c and milk production traits were weak, ranging from -0.04 to 0.23, with the highest correlations being with fat yield and fat percentage, which ranged across parities from 0.12 to 0.23 and 0.14 to 0.21, respectively. In addition, genetic correlations between CH₄c and BW were weak, ranging from -0.04 to 0.06. Strong genetic correlations were observed between CH₄c and CO₂ concentrations, ranging from 0.81 to 0.97. Furthermore, the genetic correlations between CH₄c in different parities were high (0.86 to 0.97). The weak genetic correlations between CH₄c and production traits suggest that it is feasible to select for lower CH₄c while continuing to improve milk production and other economically important traits.