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

Introduction Enteric methane (CH 4 ) 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 CH 4 emissions produced by livestock systems. However, heterogeneity in CH 4 mitigation from 3-NOP supplementation prevents livestock producers from determining the actual impact of supplementation on CH 4 emissions. This meta-analysis aimed to understand the variables responsible for the heterogeneity in CH 4 mitigation from 3-NOP supplementation in confinement-fed beef and dairy cattle. Methods 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 CH 4 yield. Results On average, 3-NOP supplementation reduced CH 4 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. Discussion Although studies showed a strong positive relationship between 3-NOP dose and CH 4 emissions ( P <0.0001), DMI was observed to have a greater influence of CH 4 abatement than 3-NOP dose. This suggests that the volume and timing of CH 4 production influences the availability of 3-NOP in the rumen during methanogenesis more than 3-NOP dose itself. This paper uses this understanding to develop equations that can estimate future CH 4 abatement in real farm systems, allowing producers the capacity to quantify the impact of 3-NOP on their greenhouse gas emissions and receive recognition for avoided CH 4 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 CH 4 emissions, which would provide producers with the actual volume of CH 4 emissions avoided.