Understanding heterogeneity in methane emissions from confinement-fed dairy and beef cattle supplemented with Bovaer®10: a meta-analysis

Ainslie Macdonald¹Richard Shephard^1,2Graham Hepworth³Richard Eckard^1*

• ¹School of Agriculture, Ecosystem, Food and Forest Sciences, Faculty of Science, The University of Melbourne, Melbourne, Australia
• ²Herd Health Pty Ltd, Maffra, Australia
• ³Statistical Consulting Centre, The University of Melbourne, Melbourne, Australia

Enteric methane (CH4) emissions from ruminant livestock production systems pose a significant challenge to efforts to mitigate global climate change. The novel feed additive 3-nitrooxypropanol (3-NOP) has the capacity to inhibit rumen methanogenesis and significantly reduce the volume of enteric CH4 emissions produced by livestock systems. However, heterogeneity in CH4 mitigation from 3-NOP supplementation prevents livestock producers from determining the actual impact of supplementation on CH4 emissions. This meta-analysis aimed to understand the variables responsible for the heterogeneity in CH4 mitigation from 3-NOP supplementation in confinement-fed beef and dairy cattle. Using 30 in vivo studies (83 treatments) that continuously supplemented 3-NOP at a range of doses from 40mg to 338mg dose (mg 3-NOP/kg dry matter intake; DMI), a mixed-effects multistep regression examined the impact of 3-NOP supplementation on CH4 yield. On average, 3-NOP supplementation reduced CH4 yield by 25.9% in beef cattle and 26.4% in dairy cattle, at the recommended dose of 60mg 3-NOP/kg DMI. Results showed that the anti-methanogenic potential of 3-NOP was influenced by 3-NOP dose (mg 3-NOP/kg DMI) and DMI kg/head-1/day-1. Despite a clear and significant relationship with 3-NOP dose (P <0.0001), DMI was observed to have a greater influence of CH4 abatement than 3-NOP dose, suggesting that the primary driver of the availability of 3-NOP in the rumen during CH4 production arises not from 3-NOP dose, but the volume and timing of CH4 production. This paper uses this understanding of the relationship between 3-NOP, DMI, and CH4 to develop equations capable of predicting the future abatement in real farm systems. To allow producers to quantify the impact of 3-NOP on their greenhouse gas emissions and receive recognition for avoided CH4 emissions. However, these equations are highly influenced by DMI and are only suitable for confinement-fed systems that consume an equal or greater volume of ration and are not a substitute for measuring CH4 emissions, which would provide producers with the actual volume of CH4 emissions avoided.