Genetic parameters for predicted production and potential for reducing enteric methane emissions through genomic selection.

Mitigation of enteric methane emission in ruminants has become an important area of research because accumulation of methane is linked to global warming. Nutritional and microbial opportunities to reduce methane emissions have been extensively researched, but little is known about using natural variation to breed animals with lower methane yield. This has been the topic investigated by Dr Y. De Haas and co-workers, the results published in the Journal of Dairy Science, Volume 94 of 2011, pages 6122 to 6134. The title of their paper is: Genetic parameters for predicted methane production and potential for reducing enteric emissions through genomic selection.

Measuring methane emission rates directly from animals is difficult and hinders direct selection on reduced methane emission. However, improvements can be made through selection on associated traits (e.g., residual feed intake) or through selection on methane predicted from feed intake and diet composition. The objective of the study, therefore, was to establish phenotypic and genetic variation in predicted methane output, and to determine the potential of genetics to reduce methane emissions in dairy cattle.

Experimental data were used and records on daily feed intake, weekly body weights, and weekly milk production were available from 548 heifers. Residual feed intake (Megajoules per day) is the difference between net energy intake and calculated net energy requirements for maintenance as a function of body weight and for fat- and protein-corrected milk production. Predicted methane emission (gram per day) is 6% of gross energy intake if corrected for the energy content of methane, which is 55.65 kilojoules per gram. The estimated heritabilities for predicted methane emission and residual feed intake were 0.35 and 0.40, respectively. The positive genetic correlation between residual feed intake and predicted methane emission indicated that cows with lower residual feed intake have lower predicted methane emission (estimates ranging from 0.18 to 0.84). Hence, it is possible to decrease the methane production of a cow by selecting more efficient cows, and the genetic variation suggests that reductions in the order of 11 to 26% in 10 years are theoretically possible, and could be even higher in a genomic selection program.

Although this is positive, there are however several uncertainties; for example, the lack of true methane measurements (and the current key assumption that methane produced per unit feed is not affected by residual feed intake level), as well as the limitations of predicting the biological consequences of selection. To overcome these limitations, an international effort is required to bring together data on feed intake and methane emissions of dairy cows. In addition, in South Africa it has become critical that we select directly for efficiency to limit input costs, rather than only for milk yield. This can be done through residual feed intake, which according to the study of Dr De Haas and colleagues, will probably reduce enteric methane production and therefore the carbon footprint of the dairy industry.