A Meta-analysis Of Enteric Methane Emissions From Beef Cattle Under Different Feeding Systems

Methane emissions from ruminants occupy 33%of anthropogenic origin.Researches have been recently focused to identify the factors such as feed intake,diet composition and digestibility that would influence the enteric methane（CH₄）emissions.Among CH₄ mitigation strategies proposed,dietary-nutritional manipulation seemed to be the most feasible.A systematic review and meta-analysis approach were used to assess the enteric methane emission in beef cattle under different feeding systems around the world in this study.Twenty-two publications reporting 62 experimental groups were included in the review stratified by a priori defined diet types based on the percentage of forage:1)forage>70%（n=31）,2)forage 70%-15%（n=18）and 3)forage<15%（n=13）.Random effect meta-analysis（MA）and meta-regressions were performed with the mean CH₄ emission values obtained from each included study stratified by feed type.Results from the MA showed that mean overall CH₄ emissions were 140.0 g/head/d,171.52 g/head/d and 193.40 g/head/d for diets classified as forage<15%,forage 15%-70%and forage>70%,respectively.Between study heterogeneities were high for all groups of studied diets（I²>95%;P<0.01）.Forage ratio and bodyweight significantly influenced the CH₄ emissions（P<0.05）.None of the production system related variables such as animals age or breed,type of study design,sample size or laboratory methodology,showed a significant relationship with enteric methane production（P>0.05）.