Sustainability & efficiency

Incorporating Alternative Methane Metrics into Sheep Breeding Objectives: Implications for Genetic Gain and Emission Efficiency

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Abstract

While absolute methane output is typically reported as the primary methane measurement, concurrent data on feed intake, body size, or growth allow methane to be expressed as alternative metrics such as yield or intensity traits, offering different perspectives on emission efficiency. However, the suitability of such traits for inclusion in breeding objectives remains unclear. This study aimed (1) to estimate genetic parameters for alternative definitions of methane emissions in a multibreed sheep population and (2) to evaluate the appropriateness of including each definition within a selection index framework. A total of 13,457 methane records were available from 7,032 animals measured across 101 flocks, representing both pedigree and crossbred sheep. Methane was measured using portable accumulation chambers (PAC). Weight measurements coincided with methane measurements, enabling calculation of methane production (g CH₄/day) and methane intensity (g CH₄/kg metabolic body weight, MBW). (Co)variance components were estimated using a linear mixed model; fixed effects included sex, breed covariates (Texel, Belclare, Suffolk, Charollais, Cheviot, and Lleyn), heterosis, recombination loss, and contemporary group of flock-date-lot of measurement. Genetic analyses used an H⁻¹ matrix comprising 330,484 animals, of which 40,685 were genotyped. Heritability for methane production was moderate (h² = 0.38), while methane intensity was lower (h² = 0.28), indicating that ratio scaling reduced additive variance. A strong correlation (r = 0.81) was observed between methane estimated breeding values (EBVs) for both traits, although only 58 animals appeared within the lowest 100 emitters across both traits, showing notable re-ranking. The genetic correlation between absolute methane production and weight was 0.46, confirming a positive relationship between numerator and denominator in the ratio trait.Three selection index scenarios were evaluated to assess expected genetic change per generation. The baseline index, reflecting the current Sheep Ireland terminal index with no explicit methane weighting, favoured faster-finishing, heavier animals but increased methane emissions (+1.22 g CH₄/day per generation). Two alternative indexes were then developed by applying a 5% weighting on either absolute methane production or methane intensity. Introducing this weighting on absolute methane production reversed the trend, reducing emissions by 0.79 g CH₄/day per generation, but resulted in slightly slower growth and reduced carcass gains. In contrast, applying the weighting to methane intensity achieved only a minor reduction in methane intensity (−0.0046 g/kg per generation) while total emissions increased slightly (+0.78 g CH₄/day per generation), favouring heavier, faster-finishing animals. Across scenarios, including methane traits led to a modest reduction in dry matter intake compared with the baseline index.Results show that both absolute methane production and methane intensity are heritable but produce divergent selection outcomes. This suggests that different methane definitions capture distinct biological and genetic variation and require careful evaluation before inclusion in breeding objectives.

Keywords: 2026

How to Cite:

Kelly, D., McGovern, F., McHugh, N., Pabiou, T. & Purfield, D., (2026) “Incorporating Alternative Methane Metrics into Sheep Breeding Objectives: Implications for Genetic Gain and Emission Efficiency”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285372. doi: https://doi.org/10.31274/wcgalp.23662

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