Repeatability and genetic parameters for phenotypes of methane emission in crossbred beef × dairy slaughter calves

Crossbreeding beef sires with dairy cows to produce beef × dairy calves is becoming increasingly common. To incorporate CH₄ reduction into breeding objectives, it is essential to accurately measure related traits and phenotypes in a sufficient number of animals to capture genetic variation. This paper will outline a method for phenotyping CH₄ in growing beef × dairy calves using a sniffer system, while also integrating growth and feed intake data. The objectives of this study were to investigate the repeatability of methane phenotypes measured by a non-intrusive sniffer setup in slaughter calf production, focusing on beef × dairy crossbred calves. Genetic parameters and heritabilities were estimated for the methane phenotypes. The study involved 9 113 beef × dairy offspring sired by Danish Blue, Charolais or Angus sires to Holstein dams. An IR gas sensor was installed in automatic feed intake recorder boxes to measure CH₄ and CO₂ gas concentration during feeding visits. Concentrations of CH₄ and CO₂ over feed box visit time were summarised as the mean, median, mean of peak concentrations observed during eructations, and the total area under the curve. Live weight and feed intake were also recorded to permit calculations of daily methane production. The repeatability of phenotype measurements on a per-visit basis, as well as their daily and weekly means, were analysed using a genetic sire-dam model. Repeatable variation was found for all traits of CH₄ and CO₂ concentration, and repeatability increased when summarising phenotypes from visits to daily and weekly means. Summarising CH₄ and CO₂ concentration by mean across visit showed higher repeatability than alternative methods. Weekly mean concentrations of CH₄ and CO₂ showed the highest repeatability of investigated methods comparable to estimates found using GreenFeed and respiration chambers. Moderate heritabilities of the sire and dam components were found for live weight, DM intake, CH₄ concentration, and CO₂ concentration. Daily methane production had a heritability of 0.28 (SE 0.07) for the sire component and 0.18 (SE 0.07) for the dam component when estimated by the ratio between CH₄ and CO₂ concentrations and information on live weight and growth. Genetic correlations did not show significant differences for sire and dam components. The study shows that there is repeatable and heritable variation in methane emission traits in beef × dairy slaughter calves, indicating that this can be included in future breeding goals for beef sires to use in beef × dairy matings.