Are methane sniffer phenotypes useful for genetic ranking of dairy cattle?

Several countries collect phenotypes for enteric methane (CH4) emissions, aiming to publish official breeding values in 2025. For genetic evaluations to be accurate, large-scale information on individual CH4 emissions is crucial. However, gold standard methods such as respiration chambers (RC) can only be used on a small scale. Proxy methods are more suitable for broad use (e.g., sniffers are gaining popularity with &gt;100 installations on commercial farms worldwide). However, sniffers measure CH4 concentrations rather than absolute emissions, which raises the question whether this impacts the genetic ranking of animals compared with other methods. This literature review and internal data<br/>analysis (Table 1) found that phenotypic correlations between sniffers and GreenFeed (GF) data were moderate (0.19–0.30). Using a phenotypic mixed model yielded moderate to strong correlations between sniffers and GF or RC (0.37–0.89), showing the environmental influence. A Dutch study reported high genetic correlations (rg; 0.71–0.76) between sniffers and GF data, where an across-country analysis showed moderate to high rg (0.50–0.72) but with high standard errors, indicating mixed models benefited from the relationship matrix for ranking animals. Enhancing processing (e.g., detection of CH4 signals) of raw<br/>sniffer data can increase the heritability, and larger datasets are likely to improve genetic parameter estimation. However, obtaining large datasets from RC is challenging. In conclusion, sniffers enable large scale phenotyping of CH4 for genetic evaluations, but data processing and modeling are important to ensure accurate ranking.