Literature survey of the influence of dietary fat composition on methane production in dairy cattle

The quantitative influence of dietary fat composition on methane production in dairy cows was estimated from a literature survey involving thirty-seven diets from seven papers. With this database covering a large range for animal performances and dietary lipid composition, it seems that methane production (expressed as 1/kg DMI of feed) decreased when either the level of production of the animals or the dietary ether extract content increased. Moreover, the database analysis pointed out that the methane decrease was only due to the fatty acid part of the ether extract and allowed to statistically quantifying this diminution which was proportional to the degree of unsaturation of the fatty acids. This compilation of experiments allowed the proposal of an index of unsaturation to improve the estimation of methane production in vivo by ruminants. The addition of unsaturated fats might be of interest for decreasing methane production, but it also might have adverse effects, such as the increase of feed refusals or the reduction in cellulose digestion. (C) 2003 Elsevier Science B.V. All rights reserved.