Can concentrations of trans octadecenoic acids in milk fat be used to predict methane yields of dairy cows?

Abstract

There is a need to develop simple, accurate methods for predicting methane emissions, yields and intensities of dairy cows. Several studies have focussed on the relationship between the concentrations of trans-10 plus trans-11 C18:1 fatty acids in milk fat and methane yield. The aim of the present study was to perform a meta-analysis to quantify relationships between the concentrations of various trans isomers of C18:1 in milk fat and methane emissions (g/day), methane yield (g/kg dry-matter intake) and methane intensity (g/kg energy-corrected milk yield). Data were from seven experiments encompassing 23 different diets and 220 observations of milk fatty acid concentrations and methane emissions. Univariate linear mixed-effects regression models were fitted to the data with the linear term as a fixed effect and with experiment and observation within experiment as random effects. Concentrations of trans-9, trans-10, trans-11 and trans-10 plus trans-11 isomers of C18:1 were poorly related to methane emissions, yields and intensities, with the best relationships being between trans-10 C18:1 and methane emissions (R2 = 0.356), trans-10 C18:1 and methane yield (R2 = 0.265) and trans-10 plus trans-11 C18:1 and methane intensity (R2 = 0.124). The data indicated that the relationships between trans-10 C18:1 and methane metrics were not linear, but were biphasic and better described by an exponential model. However, even exponential models poorly fitted the data. It is concluded that the concentrations of trans isomers of C18:1 have limited potential to accurately predict methane emissions, yields or intensities of dairy cows.