A Transformation From Methane Concentration From Sniffers to Methane Production for Implementation in Breeding Programs and Comparison With Tier 2 Equation

Reducing methane emissions from dairy cattle has gained considerable attention due to its dual benefits of improving feed efficiency and mitigating climate change. Consequently, phenotyping methane emissions in dairy populations has become increasingly important to enable direct genomic selection for lower methane emissions in breeding programs. Sniffer devices are receiving growing attention and are currently being deployed on commercial farms. However, these devices do not measure airflow and therefore provide methane concentration measurements rather than direct estimates of methane production. In this study, a new method is proposed to estimate individual cow methane production from sniffer device data that does not rely on regression on production traits and can therefore be classified as a Tier 3 approach. This novel methane production trait was derived using sniffer measurements collected in two dairy cattle populations: Spain (n = 1576) and The Netherlands (n = 2470). The proposed trait was compared with two alternative methane production estimates derived from production traits, representing a Tier 2 and an existing Tier 3 method. Phenotypic correlations between the Tier 3 traits were high (R > 0.90), whereas correlations between the Tier 2 and Tier 3 methods were substantially lower, ranging from 0.04 to 0.44. Strong agreement was observed between herd-level averages of the Tier 3 traits, while discrepancies between Tier 2 and Tier 3 estimates were more pronounced. Overall, the Tier 2 equation yielded higher methane production estimates than those obtained from sniffer-based Tier 3 traits. Heritability estimates for the Tier 3 traits ranged from 0.06 to 0.13, whereas a higher heritability (0.18-0.22) was observed for the Tier 2 trait, with standard errors between 0.02 and 0.03. Repeatability estimates were greater for the Tier 3 traits, with values ranging from 0.54 to 0.58 in Spain and from 0.25 to 0.29 in The Netherlands. The Tier 2 trait also exhibited a high repeatability (0.55-0.80). We propose this new sniffer-based Tier 3 trait as an alternative methane production phenotype that is not derived from individual production traits, thereby reducing the risk of spurious associations between methane emissions and yield-related traits. The proposed phenotype showed strong agreement with previously used Tier 3 traits and exhibited comparable heritability estimates. Nevertheless, several limitations must be acknowledged. In particular, this trait provides an estimate of methane production rather than a direct measurement, as current sniffer devices cannot capture the complete expiration or eructation plume. Despite these limitations, the trait enables the estimation of genetic trends and the prediction of breeding values expressed in biologically meaningful units. As such, it represents a valuable tool for supporting mitigation strategies and informing breeding policies aimed at reducing methane emissions from dairy cattle.