Assessing methane production and feed efficiency in both growing and mature ovine animals in six countries across Europe, South America and Oceania

Understanding key animal performance and nuisance factors associated with methane (CH4) output and feed intake is crucial in developing greenhouse gas mitigation strategies and incorporating these traits into international sheep breeding goals. The objectives of the current study were to: 1) investigate animal and nuisance (environmental + management) factors associated with CH4 output and feed intake; and 2) determine relationships between CH4 output and feed efficiency in sheep and whether or not they differ by country. Methane output was measured in sheep in Ireland, Norway, New Zealand (NZ) and Uruguay using portable accumulation chambers (PAC), and in France using GreenFeed technology. Individual feed intake was quantified using various techniques across six countries (Ireland, United Kingdom, Norway, France, Uruguay, NZ), on sheep housed indoors, grazing outdoors, and consuming forage or a total mixed ration. Studies varied by sheep breed and age, as well as feed types and measurement methods; factors associated with the variability in CH4 output and feed intake therefore differed by country. Despite variation between studies, phenotypic relationships among CH4, carbon dioxide (CO2), feed intake, feed efficiency, and live weight, were broadly similar across countries. Correlations with CH4 output (g/d) were consistent and moderate with live weight (r = 0.41–0.55); variable with dry matter intake (DMI), ranging from 0.24 (France) to 0.88 (Norway); and consistently weak with residual feed intake (RFI). Correlations with CO2 output (g/d) were consistent with live weight gain (r = 0.57) where estimated (France, Uruguay); variable with DMI, from moderate (r = 0.48 for France to r = 0.54 for NZ) to high (r = 0.71, Uruguay); and weak (r = 0.12, Uruguay) to moderately weak (r = 0.21, France) with RFI. Despite disparate datasets, combining data facilitates comparison and discussion on methodologies and interpretation of results. Results support the hypothesis that specific biological processes govern some trait relationships, being independent of factors like breed, age and feed, but that other relationships (e.g. between CO2 and feed intake) are potentially strongly influenced by methodology and warrant further investigation. This is pertinent as we seek feed intake proxies to allow the estimation of CH4 yield, an important metric in international CH4 accounting.