Breeding for reduced methane emission and feed-efficient Holstein cows: An international response.

Discipline: environment; Keywords:  methane production, residual methane, methane yield, feed efficiency.

Reducing methane emissions in livestock production is one of the challenges of this century and researchers from different disciplines including nutrition, physiology, and genetics have made substantial efforts to develop tools that can help reduce methane emissions. Methane traits in dairy cattle have low to moderate heritability, from 0.11 to 0.33. Consequently, selecting for animals with low methane emissions should be a necessary approach, given that genetic progress is permanent and cumulative over generations. Genetic selection, however, requires a large number of animals with records to predict accurate breeding values. Currently, the data available on methane emissions are scarce or nonexistent in most countries, as measuring methane is expensive and labour intensive. Therefore, combining data from different countries is an attractive solution to increase data set size, thereby improving accuracy of genetic parameters for methane production, compared with only using data from one country. Additionally, genetic correlations with economically important traits can be estimated more accurately, making it possible to include methane traits in future breeding. This was the intention of the study reported by Dr C.I V. Manchanilla-Pech and co-workers, the results of which were published in the Journal of Dairy Science, Volume 104 of 2021, page 8983 to 9001. The title of the paper is: Breeding for reduced methane emission and feed-efficient Holstein cows: An international response.

A total of 15 320 methane production records in g per day from 2 990 cows belonging to four countries (Canada, Australia, Switzerland, and Denmark) were analyzed. Records on dry matter intake (DMI), body weight (BW), body condition score (BCS), and milk yield (MY) were also available. Additional traits such as methane yield (g per kg DMI), methane intensity (g per kg energy-corrected milk), a genetic standardized methane production, and three definitions of residual methane production (g per day), residual feed intake, metabolic BW (MBW), BW change, and energy-corrected milk were also calculated.

The estimated heritability of methane production was 0.21, whereas heritability estimates for methane yield and methane intensity were 0.30 and 0.38, and for the residual methane traits heritability ranged from 0.13 to 0.16. Genetic correlations between different methane traits were moderate to high (0.41 to 0.97). Genetic correlations between methane production and economically important traits ranged from 0.29 (MY) to 0.65 (BW and MBW), being 0.41 for DMI. Selection index calculations showed that residual methane had the most potential for inclusion in the breeding goal when compared with methane production, yield and intensity, as residual methane allows for selection of low methane emitting animals without compromising other economically important traits. Inclusion of residual feed intake in the breeding goal could further reduce methane, as the correlation with residual methane is moderate and elicits a favourable correlated response. Adding a negative economic value for methane could facilitate a substantial reduction in methane emissions while maintaining an increase in milk production.

Conclusions: Methane is highly correlated with other economically important traits such as milk production, weight, and feed intake. For this reason, it is important to have a trait that is adjusted for the production traits. Residual methane adjusted by MBW and energy corrected milk appears to be the best option, given that the genetic correlations are close to zero with its regressors and DMI. Residual methane is also positively correlated with residual feed intake, implying that lower methane-emitting animals are also more efficiently converting feed.