Genetic and environmental variation in methane emissions of sheep at pasture1

Abstract

A total of 2,600 methane (CH 4 ) and 1,847 CO 2 measurements of sheep housed for 1 h in portable accumulation chambers (PAC) were recorded at 5 sites from the Australian Sheep CRC Information Nucleus, which was set up to test leading young industry sires for an extensive range of current and novel production traits. The final validated dataset had 2,455 methane records from 2,279 animals, which were the progeny of 187 sires and 1,653 dams with 7,690 animals in the pedigree file. The protocol involved rounding up animals from pasture into a holding paddock before the first measurement on each day and then measuring in groups of up to 16 sheep over the course of the day. Methane emissions declined linearly (with different slopes for each site) with time since the sheep were drafted into the holding area. After log transformation, estimated repeatability (rpt) and heritability (h 2 ) of liveweight-adjusted CH 4 emissions averaged 25% and 11.7%, respectively, for a single 1-h measurement. Sire × site interactions were small and nonsignificant. Correlations between EBV for methane emissions and Sheep Genetics Australia EBV for production traits were used as approximations to genetic correlations. Apart from small positive correlations with weaning and yearling weights (r = 0.21-0.25, P < 0.05), there were no significant relationships between production trait and methane EBV (calculated from a model adjusting for liveweight by fitting separate slopes for each site). To improve accuracy, future protocols should use the mean of 2 (rpt = 39%, h 2 = 18.6%) or 3 (rpt = 48%, h 2 = 23.2%) PAC measurements. Repeat tests under different pasture conditions and time of year should also be considered, as well as protocols measuring animals directly off pasture instead of rounding them up in the morning. Reducing the time in the PAC from 1 h to 40 min would have a relatively small effect on overall accuracy and partly offset the additional time needed for more tests per animal. Field testing in PAC has the potential to provide accurate comparisons of animal and site methane emissions, with potentially lower cost/increased accuracy compared to alternatives such as SF 6 tracers or open path lasers. If similar results are obtained from tests with different protocols/seasonal conditions, use of PAC measurements in a multitrait selection index with production traits could potentially reduce methane emissions from Australian sheep for the same production level.

Application of meta-omics techniques to understand greenhouse gas emissions originating from ruminal metabolism

“…If it can be demonstrated that the different volumes of methane emissions from different animals can be explained by their differing ruminal microbiomes, and that the property is persistent and heritable, it should be possible to select future generations of cattle and sheep that have genetically determined lower methane emissions. Thus far, it has been demonstrated that methane emissions in sheep [14, 15, 17], dairy cows [18] and beef steers [19, 20] are significantly heritable. Indeed, the prediction of methane emissions via milk fatty acid composition, as described below, is heritable [21].…”

Oral Samples as Non-Invasive Proxies for Assessing the Composition of the Rumen Microbial Community

“…There is a pressing need to carry out large-scale ruminal microbiome analysis to generate a microbial phenotype for use as a trait in future animal selection for rumen function, including methanogenesis [ 6 , 42 ], feed conversion efficiency [ 6 , 42 , 43 ] and health [ 6 , 44 , 45 ]. Both methanogenesis and feed conversion efficiency have major implications on the environmental impact of ruminant livestock production [ 2 , 6 ].…”

Benefits of including methane measurements in selection strategies

“…The genetic parameter estimates compiled in the Supplemental Material show that MP is strongly related to weight and DFI, with somewhat stronger relationships observed for RC measurements (especially under restricted feeding protocols in which the amount of feed offered is a function of live weight) than PAC. The phenotypic relationship between weight and PAC measurements of MP was noted to differ between sites with no consistent overall relationship across all sites (Robinson et al, 2014a), suggesting that MPadjWt might prove a more robust selection criterion.…”

“…To reduce the dependence on weight, RC measurements are often expressed as methane yield (my), calculated as methane emissions per kilogram of DMI. By contrast, measurements of grazing animals are often adjusted for live weight to avoid favoring smaller animals that would be expected to eat less and therefore emit less methane than their larger herd mates (Robinson et al, 2014a).…”