Mitigation of greenhouse gases in dairy cattle via genetic selection: 2. Incorporating methane emissions into the breeding goal.

The objective of this study was to analyze the impact of incorporating enteric methane into the breeding objective of dairy cattle in Spain, and to evaluate both genetic and economic response of traits in the selection index under 4 scenarios: (1) the current ICO (Spanish total merit index), used as benchmark; (2) a hypothetical penalization of methane emissions through a carbon tax; (3) considering methane as a net energy loss for the animal; and (4) desired genetic response to reduce methane production by 20% in 10 yr. A bio-economic model was developed to derive the economic values for production and methane traits in each scenario. The estimated economic values for methane were estimated at -€1.21/kg and -€0.32/kg for scenarios 2 and 3, respectively. When merged with other traits in the selection index, methane had less economic importance (1-5%) than milk protein yield (39-42%) or milk fat yield (27-28%). Under these scenarios, selection resulted in an unfavorable response in methane emissions when it was included with an economic weight, with an increase in methane estimated from 0.52 to 0.60 kg/cow per year. Small differences in total profit per cow per year were observed between indices. The incorporation of methane production into the breeding objective had a negligible effect on production, with minor reductions in the expected genetic gain for fat and protein yields and in total economic benefits. However, total methane emissions in the dairy industry in Spain were estimated to decrease between 2 and 5% in the next 10 yr due to positive genetic trends for milk yield and an expected decrease in the total number of dairy cows. Additionally, methane intensity per 1 billion liters of milk would decrease in all scenarios. The uncertainty in the genetic parameters of methane and in carbon prices were tested in a sensitivity analysis, resulting in small deviations from the benchmark scenario. A major effect was observed only under the desired genetic response scenario. In this case, it was possible to achieve a 20% reduction of methane production in 10 yr via selective breeding but at the expense of a larger ad hoc weight (33%) of methane in the selection index and decelerating the genetic gain for production traits from 6 to 18%. This study shows the potential of including environmental traits in the selection indices while retaining populations profitable for producers.

Mitigation of greenhouse gases in dairy cattle via genetic selection: 1. Genetic parameters of direct methane using noninvasive methods and proxies of methane.

Records of methane emissions from 1,501 cows on 14 commercial farms in 4 regions of Spain were collected from May 2018 to June 2019. Methane concentrations (MeC) were measured using a nondispersive infrared methane detector installed within the feed bin of the automatic milking system during 14- to 21-d periods. Rumination time (RT; min/d) was collected using collars with a tag that registered time (minutes) spent eating and ruminating. The means of MeC and methane production (MeP) were 1,254.28 ppm and 182.49 g/d, respectively; mean RT was 473.38 min/d. Variance components for MeC, MeP, and RT were estimated with REML using pedigree and genomic information in a single-step model. Heritabilities for MeC and MeP were 0.11 and 0.12, respectively. Rumination time showed a slightly larger heritability estimate (0.17). The genetic correlation between MeP and MeC was high (>0.95), suggesting that selection on either trait would lead to a positive correlated response on the other. Negative correlations were estimated between RT and MeC (-0.24 ± 0.38) and MeP (-0.43 ± 0.35). Methane concentration and MeP had slightly positive correlations with milk yield (0.17 ± 0.39 and 0.21 ± 0.36), protein percentage (0.08 ± 0.32 and 0.30 ± 0.45), protein yield (0.22 ± 0.41 and 0.31 ± 0.35), fat percentage (0.02 ± 0.40 and 0.27 ± 0.36), and fat yield (0.27 ± 0.28 and 0.29 ± 0.28) from bivariate analyses. Rumination time had positive correlations with milk yield (0.41 ± 0.75) and protein yield (0.26 ± 0.57) and negative correlations with fat yield (-0.45 ± 0.32), protein percentage (-0.15 ± 0.38), and fat percentage (-0.40 ± 0.47). A positive approximated genetic correlation was estimated between fertility and MeC (0.10 ± 0.05) and MeP (0.18 ± 0.05), resulting in slightly higher CH4 production when selecting for better fertility [days open estimated breeding values (EBV) are expressed with mean 100 and SD 10, inversely related to days from calving to conception; that is, greater days open EBV implies better fertility]. Positive correlations were also estimated for stature with MeC and MeP (0.30 ± 0.04 and 0.43 ± 0.04, respectively). Other type traits (chest width, udder depth, angularity, and capacity) were positively correlated with methane traits, possibly because of higher milk yield and higher feed intake from these animals. Rumination time showed positive EBV correlations with production traits and type traits, and negative correlations with somatic cell count and body condition score. Based on the genetic correlations and heritabilities estimated in this study, methane is measurable and heritable, and estimates of genetic correlations suggest no strong opposition to current breeding objectives in Spanish Holsteins.