Invited review: Large-scale indirect measurements for enteric methane emissions in dairy cattle: A review of proxies and their potential for use in management and breeding decisions.
Efforts to reduce the carbon footprint of milk production through selection and management of low-emitting cows require accurate and large-scale measurements of methane (CH4) emissions from individual cows. Several techniques have been developed to measure CH4in a research setting but most are not suitable for large-scale recording on farm. Several groups have explored proxies (i.e., indicators or indirect traits) for CH4; ideally these should be accurate, inexpensive, and amenable to being recorded individually on a large scale. This review (1) systematically describes the biological basis of current potential CH4proxies for dairy cattle; (2) assesses the accuracy and predictive power of single proxies and determines the added value of combining proxies; (3) provides a critical evaluation of the relative merit of the main proxies in terms of their simplicity, cost, accuracy, invasiveness, and throughput; and (4) discusses their suitability as selection traits. The proxies range from simple and low-cost measurements such as body weight and high-throughput milk mid-infrared spectroscopy (MIR) to more challenging measures such as rumen morphology, rumen metabolites, or microbiome profiling. Proxies based on rumen samples are generally poor to moderately accurate predictors of CH4, and are costly and difficult to measure routinely on-farm. Proxies related to body weight or milk yield and composition, on the other hand, are relatively simple, inexpensive, and high throughput, and are easier to implement in practice. In particular, milk MIR, along with covariates such as lactation stage, are a promising option for prediction of CH4emission in dairy cows. No single proxy was found to accurately predict CH4, and combinations of 2 or more proxies are likely to be a better solution. Combining proxies can increase the accuracy of predictions by 15 to 35%, mainly because different proxies describe independent sources of variation in CH4and one proxy can correct for shortcomings in the other(s). The most important applications of CH4proxies are in dairy cattle management and breeding for lower environmental impact. When breeding for traits of lower environmental impact, single or multiple proxies can be used as indirect criteria for the breeding objective, but care should be taken to avoid unfavorable correlated responses. Finally, although combinations of proxies appear to provide the most accurate estimates of CH4, the greatest limitation today is the lack of robustness in their general applicability. Future efforts should therefore be directed toward developing combinations of proxies that are robust and applicable across diverse production systems and environments.
Biometrical Genetics, Green Technology, Natural Resources Institute Finland (Luke), FIN-31600 Jokioinen, Finland. Electronic address: Enyew.negussie@luke.fi.
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Negussie
Animal Breeding and Genomics Centre of Wageningen Livestock Research, PO Box 338, NL-6700 AH Wageningen, the Netherlands.
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de Haas
Valorisation of Agricultural Products, Walloon Agricultural Research Center (CRA-W), BEL-5030 Gembloux, Belgium.
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Dehareng
Scotland's Rural College, King's Buildings, West Mains Road, Edinburgh EH9 3JG, United Kingdom.
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Dewhurst
Animal Nutrition Group, Wageningen University and Research, PO Box 338, NL-6700 AH Wageningen, the Netherlands.
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Dijkstra
Agriculture, Bio-engineering and Chemistry, Gembloux Agro-Bio Tech, University of Liège, BEL-5030 Gembloux, Belgium.
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Gengler
UMR1213 Herbivores, INRA, Vetagro Sup, 63122, Saint-Genès-Champanelle, France.
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Morgavi
Agriculture, Bio-engineering and Chemistry, Gembloux Agro-Bio Tech, University of Liège, BEL-5030 Gembloux, Belgium.
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Soyeurt
Animal Nutrition Group, Wageningen University and Research, PO Box 338, NL-6700 AH Wageningen, the Netherlands.
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van Gastelen
Agri-Food and Biosciences Institute, Hillsborough, Co. Down BT26 6DR, United Kingdom.
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Yan
Department of Bioinformatics, PTP Science Park, Via Einstein Loc. Cascina Codazza, 26900 Lodi, Italy; Faculty of Bioscience and Technology for Food, Agriculture and Environment, University of Teramo, via R. Balzarini 1 64100 Teramo, Italy.
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Biscarini
D000818:Animals; D001947:Breeding; D002417:Cattle; D005260:Female; D007774:Lactation; D008697:Methane / Q000096:biosynthesis*; D008892:Milk / Q000737:chemistry; D012417:Rumen / Q000378:metabolism
D008697:Methane
breeding; dairy cattle; enteric methane; management; proxy