Mitigation of greenhouse gases in livestock via genetic selection: incorporation of methane emissions into the breeding goal in dairy cattle under different scenarios

The objective of this study was to analyze the impact of the incorporation of enteric methane (CH4) into the breeding objective of dairy cattle in Spain, and to evaluate both genetic and economic response of traits in the selection index under foreseen scenario, that aims to reduce the carbon footprint of enteric CH4 in dairy cattle in terms of lower CH4 emissions: i. Current situation as benchmark (without putting an economic value on CH4 emissions); ii. Penalization of CH4 emissions through a carbon tax; iii. CH4 emissions in a carbon quota; and iv. Including CH4 as a net energy loss cost. In order to include CH4 emission as a breeding goal, one of the first tasks is to define the economic importance of each trait included in the aggregate genotype and his economic weighting in the current and planned situation. Thus, economic value (EV) of CH4 emissions, which represents a loss of dietary energy in ruminants and is an important contributor to global warming, needed to be estimated. To achieve this, first we developed a bio economic model to derive the EV for production and CH4 traits. Then we estimated variance components for CH4 as well as its genetic correlations with other traits in the Total Merit Index (ICO). Finally, we calculated the genetic and economic responses to selection for each scenario that has been tested. The estimated EVs are 0.01, 1.94, and 4.48 (Euros per kg) for milk volume, milk fat and milk protein yields in scenario 1. For CH4, the economic values are calculated as - 1.21, -9.32 and -0.67 (Euros per kg) for scenarios 2, 3 and 4, respectively. The estimated heritability for CH4 is 0.38 plus minus 0.16, showing that CH4 is a heritable trait in dairy cattle. The genetic correlations between CH4 and the traits in the ICO, and between CH4 and the ICO are generally low and negative, suggesting that has been selecting for better efficiency that leads to lower CH4 emissions from lactating cows, and that more profitable cows produce less CH4. All of the studied indices resulted in a favorable response in overall CH4 emissions ranging from a reduction of -0.51 kg per cow per year with the current index, to - 0.70, -0.86, and -2.41 kg per cow per annum respectively for the three environmental indices: CO2 tax, CH4 quota and net energy loss cost. On the other hand, the incorporation of CH4 to the baseline index, generates an increase in benefit of 38.35 Euros per cow per yr. this benefit was negligibly changed in the case of CO2 tax and net energy loss scenarios, whilst in the situation of CH4 quota, the overall economic response of the index falls to 33.87 Euros per cow per yr (-21 per cent). The sensitivity analysis, considering the variation when different key parameters and CH4 was included into the breeding goal under each scenario, showed that both the total benefit and genetic responses are insensitive to the changes. Except for the case of CH4 quota, the genetic responses are highly sensitive when the economic weights and genetic correlations of CH4 with other traits were varied. This study showed that there is a potential in mitigating CH4 emissions by genetic selection through the inclusion of CH4 in selection objectives of dairy cattle while remaining profitable. Its inclusion in selection indices, will allow selecting for low emitting and more efficient cows.