Repeatability of methane emissions from sheep

Abstract

Breeding of ruminant livestock for low CH₄ emission is an attractive means of mitigating enteric CH₄ emissions. However success requires that the mechanism responsible for among animal variation in emissions is repeatable and heritable and has a negligible negative impact on production and functional traits. This study was designed to estimate repeatability and heritability of the CH₄4 emission trait in sheep, and to determine whether the ranking of sheep based on their CH₄ emissions is maintained over a range of contrasting diets. A flock of 105 ewe lambs (10 months old) of a progeny testing program were screened for their CH₄ yields (i.e., emissions/unit feed dry matter (DM) intake) when a molasses containing grass silage was fed at restricted intake (1.3 x maintained 13-15 d between consecutive measurements (i.e., screening phase). Mean CH₄ yield of lambs was 18.4 ± 0.38 g/kg DM intake during the screening phase, and estimates of repeatability and heritability for CH₄ yield were 0.16 and 0.30, respectively. Methane yield in the screening phase was 7.9% higher for the high versus low ranked sheep (19.2 ± 0.18 versus 17.8 ± 0.26 g/kg DM intake). The 10 lowest (low rank) and the 10 highest (high rank) CH₄ yielding sheep were selected and retained for further study. Two repeated measurements of CH₄ yield were conducted, the first measurement while sheep were fed fresh cut perennial ryegrass pasture (grass), the second with the same sheep fed a 400:600 concentrate:forage (wheat grain:lucerne hay; fresh basis) pelleted diet (pellet). Repeated measurements revealed that rankings were maintained among diets, but that there was a CH₄ rank x diet interaction for CH₄4 yield. When fed the grass diet, the high ranked sheep had 13% higher CH₄4 yield than the low ranked sheep, but when fed the pelleted diet, the high ranked sheep had 36% higher CH₄ yield than the low ranked sheep. Emissions of hydrogen were only measurable when sheep were fed the pelleted diet. This study is the first to report that ranking of sheep for CH₄4 emissions is consistent among diets, although the magnitude of difference among the rankings was affected by diet, suggesting that among animal variation in CH₄ emission could be exploited to breed animals for low CH₄ emission.