Meta-analysis of relationships between enteric methane yield and milk fatty acid profile in dairy cattle

摘要

Various studies have indicated a relationship between enteric methane (CH_4) production and milk fatty acid (FA) profiles of dairy cattle. However, the number of studies investigating such a relationship is limited and the direct relationships reported are mainly obtained by variation in CH_4 production and milk FA concentration induced by dietary lipid supplements. The aim of this study was to perform a meta-analysis to quantify relationships between CH_4 yield (per unit of feed and unit of milk) and milk FA profile in dairy cattle and to develop equations to predict CH_4 yield based on milk FA profile of cows fed a wide variety of diets. Data from 8 experiments encompassing 30 different dietary treatments and 146 observations were included. Yield of CH_4 measured in these experiments was 21.5 ± 2.46 g/kg of dry matter intake (DMI) and 13.9 ± 2.30 g/ kg of fat- and protein-corrected milk (FPCM). Correlation coefficients were chosen as effect size of the relationship between CH_4 yield and individual milk FA concentration (g/100 g of FA). Average true correlation coefficients were estimated by a random-effects model. Milk FA concentrations of C6:0, C8:0, C10:0, C16:0, and C16:0-iso were significantly or tended to be positively related to CH_4 yield per unit of feed. Concentrations of trans-6+7+8+9 C18:l, trans-10+11 C18:l, cis-11 C18:1, cis-12 C18:1, cis-13 C18:1, trans-16+cis-14 C18:1, and cis-9,12 C18:2 in milk fat were significantly or tended to be negatively related to CH_4 yield per unit of feed. Milk FA concentrations of C10:0, C12:0, C14:0-iso, C14:0, cis-9 C14:1, C15:0, and C16:0 were significantly or tended to be positively related to CH_4 yield per unit of milk. Concentrations of C4:0, C18:0, trans-10+U C18:l, cis-9 C18:l, cis-11 C18:l, and cis-9,12C18:2in milk fat were significantly or tended to be negatively related to CH_4 yield per unit of milk. Mixed model multiple regression and a stepwise selection procedure of milk FA based on the Bayesian information criterion to predict CH_4 yield with milk FA as input (g/100 g of FA) resulted in the following prediction equations: CH_4 (g/kg of DMI) = 23.39 + 9.74·× C16:0-iso- 1.06 × trans-10+U C18:l - 1.75 × cis-9,12 C18:2 (R~2 = 0.54), and CH_4 (g/kg of FPCM) = 21.13 - 1.38 × C4:0 + 8.53 × C16:0-iso - 0.22 × cis-9 C18:l - 0.59 × trans-10+11 C18:1 (R~2 = 0.47). This indicated that milk FA profile has a moderate potential for predicting CH_4 yield per unit of feed and a slightly lower potential for predicting CH_4 yield per unit of milk.