title: Meta-analysis of relationships between enteric methane yield and milk fatty acid profile in dairy cattle.
abstract: Various studies have indicated a relationship between enteric methane (CH4) 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 CH4 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 CH4 yield (per unit of feed and unit of milk) and milk FA profile in dairy cattle and to develop equations to predict CH4 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 CH4 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 CH4 yield and individual milk FA concentration (g/100g 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 CH4 yield per unit of feed. Concentrations of trans-6+7+8+9 C18:1, trans-10+11 C18:1, 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 CH4 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 CH4 yield per unit of milk. Concentrations of C4:0, C18:0, trans-10+11 C18:1, cis-9 C18:1, cis-11 C18:1, and cis-9,12 C18:2 in milk fat were significantly or tended to be negatively related to CH4 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 CH4 yield with milk FA as input (g/100g of FA) resulted in the following prediction equations: CH4 (g/kg of DMI)=23.39 + 9.74 × C16:0-iso - 1.06 × trans-10+11 C18:1 - 1.75 × cis-9,12 C18:2 (R(2) = 0.54), and CH4 (g/kg of FPCM) = 21.13 - 1.38 × C4:0 + 8.53 × C16:0-iso - 0.22 × cis-9 C18:1 - 0.59 × trans-10+11 C18:1 (R(2) = 0.47). This indicated that milk FA profile has a moderate potential for predicting CH4 yield per unit of feed and a slightly lower potential for predicting CH4 yield per unit of milk.
authors.affiliation: TI Food and Nutrition, PO Box 557, 6700 AN Wageningen, the Netherlands; Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands. Electronic address: henk.vanlingen@wur.nl.
authors.forename: H J
authors.initials: HJ
authors.lastname: van Lingen
authors.affiliation: Division of Food Production and Quality, School of Agriculture, Policy and Development, University of Reading, Reading RG6 6AR, United Kingdom.
authors.forename: L A
authors.initials: LA
authors.lastname: Crompton
authors.affiliation: Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands; Faculty of Veterinary Medicine, Utrecht University, PO Box 80.163, 3508 TD Utrecht, the Netherlands.
authors.forename: W H
authors.initials: WH
authors.lastname: Hendriks
authors.affiliation: Division of Food Production and Quality, School of Agriculture, Policy and Development, University of Reading, Reading RG6 6AR, United Kingdom.
authors.forename: C K
authors.initials: CK
authors.lastname: Reynolds
authors.affiliation: Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Dijkstra
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements / Q000032:analysis; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D007774:Lactation; D008697:Methane / Q000378:metabolism*; D008892:Milk / Q000737:chemistry*; D008954:Models, Biological
chemical_list: D005227:Fatty Acids; D008697:Methane
keywords: dairy cattle; meta-analysis; methane; milk fatty acid profile