INTRODUCTION

1. META-ANALYSIS OF RELATIONSHIPS BETWEEN ENTERIC METHANE YIELD AND MILK FATTY ACID PROFILE IN DAIRY CATTLE INTRODUCTION Milk fatty acids (FA) partly originate from rumen processes associated with enteric CH4 production Milk FA profile and CH4 production depend on type of feed Milk FA profile and CH4 production were correlated previously based on a limited variety of diets AIM: to quantify relationships between CH4 yield (g/kg DMI) and milk FA concentrations (g/100 g FA) of dairy cows fed a wide variety of diets Statistics Correlation coefficients were chosen as effect size for the relationship between CH4 yield and milk FA concentrations Meta-analytic random-effects model, which assumes random variability among the true effect induced by study conditions: Forest plot Henk J. van Lingen1,2, Les A. Crompton3, Christopher K. Reynolds3 and Jan Dijkstra2 RESULTS AND DISCUSSION Multiple regression Mixed model to predict CH4 yield with milk FA concentrations: CH4 (g/kg DMI) = 23.39 + 9.74 × C16:0-iso – 1.06 × trans-10+11-C18:1 – 1.75 × cis-9,12-C18:2 R2 = 0.54 is lower than Dijkstra et al. (2011) obtained for their equation with R2 = 0.73 Saturated FA are all at least partly synthesized de novo (Bernard et al., 2008), which is positively associated with fiber fermentation (Bannink et al., 2008) and CH4yield. CONCLUSION Various milk FA concentrations are significantly or tend to be related to CH4 yield Potential for predicting CH4 yield with milk FA concentrations appears to be moderate MATERIALS AND METHODS Inclusion criteria for data CH4 emission measured in respiration chambers Milk FA composition elucidated by gas chromatography Dataset 4 studies from the University of Reading (UK) 4 studies from Wageningen University (NL) 30 dietary treatments and 146 observations CH4yield was 21.5 ± 2.46 g/kg DMI Correlation between CH4 yield and milk FA concentrations Correlations of OBCFA concentrations are minor or absent in line with (Chilliard et al., 2009; Mohammed et al., 2011), are less than indicated by Vlaeminck et al. (2006) Unsaturated FA (C18:3n-3, C18:2n-6, c9-C18:1 from feed; C18:1 isomers from the rumen) inhibit CH4yield (Patra, 2013), several of these FA vary in milk FA concentration References Bernard, L., C. Leroux, and Y. Chilliard. 2008. Adv. Exp. Med. Biol. 606:67-108. Bannink, A., J. France, S. Lopez, W.J.J. Gerrits, E. Kebreab, S. Tamminga, and J. Dijkstra. 2008. Anim. Feed Sci. Technol. 143:3-26. Chilliard, Y., C. Martin, J. Rouel, and M. Doreau. 2009. J. Dairy Sci. 92:5199-5211. Dijkstra, J., S.M. van Zijderveld, J.A. Apajalahti, A. Bannink, W.J.J. Gerrits, J.R. Newbold, H.B. Perdok, and H. Berends. 2011. Anim. Feed Sci. Technol. 166:590-595. Vlaeminck, B., V. Fievez, S. Tamminga, R.J. Dewhurst, A. van Vuuren, D. de Brabander, and D. Demeyer. 2006b. J. Dairy Sci. 89:3954-3964. Patra, A.K. 2013. Livest. Sci. 155:244-254.