Genetic parameters for methane emissions in Australian sheep measured in portable accumulation chambers in grazing and controlled environments

Abstract

Context. Genotype by environment interaction or sire re-ranking between measurements of methane emission in different environments or from using different measurement protocols can affect the efficiency of selection strategies to abate methane emission. Aim. This study tested the hypothesis that measurements of methane emission from grazing sheep under field conditions, where the feed intake is unknown, are genetically correlated to measurements in a controlled environment where feed intake is known. Methods. Data on emission of methane and carbon dioxide and uptake of oxygen were measured using portable accumulation chambers from 499 animals in a controlled environment in New South Wales and 1382 animals in a grazing environment in Western Australia were analysed. Genetic linkage between both environments was provided by 140 sires with progeny in both environments. Multi-variate animal models were used to estimate genetic parameters for the three gas traits corrected for liveweight. Genetic groups were fitted in the models to account for breed differences. Genetic correlations between the field and controlled environments for the three traits were estimated using bivariate models. Key results. Animals in the controlled environment had higher methane emission compared to the animals in the field environment (37.0 ± s.d 9.3 and 35.3 ± s.d 9.4 for two protocols vs 12.9 ± s.d 5.1 and 14.6 ± s.d 4.8 mL/min for lambs and ewes (±s.d); P < 0.05) but carbon dioxide emission and oxygen uptake did not significantly differ. The heritability estimates for methane emission, carbon dioxide emission and oxygen uptake were 0.15, 0.06 and 0.11 for the controlled environment and 0.17, 0.27 and 0.35 for the field environment. The repeatability for the traits in the controlled environment ranged from 0.51 to 0.59 and from 0.24 to 0.38 in the field environment. Genetic correlations were high (0.85-0.99) but with high standard errors. Conclusion. Methane emission phenotypes measured using portable accumulation chambers in grazing sheep can be used in genetic evaluation to estimate breeding values for genetic improvement of emission related traits. The combined measurement protocol-environment did not lead to re-ranking of sires. Implication. These results suggest that both phenotypes could be used in selection for reduced methane emission in grazing sheep. However, this needs to be consolidated using a larger number of animals and sires with larger progeny groups in different environments.

A meta‐analysis of the genetic contribution to greenhouse gas emission in sheep

“…The high genetic associations between CO 2 emission and O 2 consumption show that the two traits are genetically identical. The negative associations were expected since CO 2 is exhaled (positive values) from the inhaled O 2 (negative values) from the lungs (Wahinya et al, 2022). On the other hand, the low and non-significant genetic correlations of rumen concentrations of volatile fatty acids with METP indicate that volatile fatty acid concentrations are of limited utility in selecting for methane production of sheep.…”

“…Therefore, one option to mitigate these emissions is to select ruminants that emit less GHG. For the direct selection of the gas emission traits, a practical measurement protocol requires to be set up to get phenotypic information at scale on selection candidates, or on animals of a reference population that could be applied for predicting genomic breeding values (Wahinya et al, 2022). Various procedures and measurement protocols are available to measure methane emission phenotypes in sheep.…”

“…Closed‐circuit respiration chambers (Blaxter & Clapperton, 1965) and portable accumulation chambers (PAC) have been applied to measure emission in controlled and field situations, respectively (Bond et al, 2019; Goopy et al, 2016; Robinson et al, 2020). In addition to measuring methane emission by PAC, it can be applied to concurrently measure oxygen uptake and carbon dioxide production (Wahinya et al, 2022). Carbon dioxide production and oxygen uptake measured in PAC have been reported to be more heritable.…”

“…Also, they have a higher genetic association with feed intake than methane emission for sheep at different ages (Paganoni et al, 2017). Therefore, measuring these traits in sheep with PAC could be less expensive and be used as a representative for feed intake (Wahinya et al, 2022).…”

Large-scale analysis of sheep rumen metagenome profiles captured by reduced representation sequencing reveals individual profiles are influenced by the environment and genetics of the host

“…These ewes are primarily Merinos and are representative of, and have genetic links with, the genotypes currently used in the Australian sheep industry (42,43). The 488 sheep that had rumen samples came from 176 sires (44). Additional details for each sample can be found in Additional File 1.…”