Genetic parameters for enteric methane traits and their relationship with milk production in Danish Holstein and Danish Jersey Cattle

Introducing a selection index for enteric methane (CH4) emissions in<br/>dairy cattle is a key focus in animal breeding. A sustainable design of<br/>breeding schemes implies a comprehensive understanding of the genetic<br/>architecture of new traits and their relationship with existing breeding<br/>goal traits. However, most research has thus far focused on Holstein<br/>(HOL) cattle, with limited insights into other breeds. Thus, this study<br/>aimed to estimate genetic parameters for enteric CH4 traits, obtained<br/>from sniffers installed in 17 commercial Danish farms, and their genetic<br/>correlation with milk production traits. A set of 4,727 HOL and 1,900<br/>Jersey (JER) cows with 652,183 (HOL) and 231,377 (JER) daily records<br/>of milk, fat, and protein yields, as well as CH4 and CO2 concentrations,<br/>and the CH4:CO2 ratio, was used. In general, heritabilities for CH4 traits<br/>were higher for JER than for HOL: for example, h2 = 0.27 (SE = 0.06, JER) vs. h2<br/> = 0.14 (SE = 0.03, HOL) for the CH4 concentrations. For JER, genetic correlations were mostly not significant and in a low to moderate favorable direction, indicating lower emissions with higher milk production. In contrast, they were moderate to high and unfavorable for HOL. We speculate that this breed difference may be mediated by the level of feed intake. Moreover, a strong negative genetic correlation between the CH4:CO2 ratio and fat yield was found for JER (rg = −0.62, 166 J. Dairy Sci. Vol. 108, Suppl. 1 SE = 0.17), possibly indicating a relationship between these traits via the negative energy balance, as the characteristic mobilization of body fat reserves results in an increased fat yield but also higher CO2 concentration in the breath. Overall, the results of this study reveal heritable CH4 emissions, whose genetic correlation with milk production traits differs between breeds. This might be caused by metabolic differences<br/>(e.g., related to the energy balance and feed intake) but requires further<br/>clarification based on larger data sets.