Research Article Received: 31 July 2011 Revised: 7 October 2011 Accepted: 23 October 2011 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/jsfa.5525 Experimental improvement of cow milk fatty acid composition in organic winter diets † Ton Baars, a,c * Jenifer Wohlers, a Daniel Kusche a and Gerhard Jahreis b Abstract BACKGROUND: Organic milk is seen as more healthy in terms of its fatty acid (FA) profile. In three on-farm crossover trials with 10–12 cows in each group, different forages were compared for their potential to improve the FA composition. Different hay qualities (hay of pasture vs. hay of leys), additional energy sources (fodder beets vs. wheat) and roughage qualities (hay of pasture vs. grass silage) were compared for their effect on the FA composition of the milk. RESULTS: Rumenic acid (CLA cis-9, trans-11) and α-linolenic acid (ALA) were selected as principal markers to evaluate effects. The overall CLA cis-9, trans-11 was low (3.6 – 6.3 g kg -1 fat), whereas ALA levels were intermediate (6.8 – 9.4 g kg -1 fat). Differences between the forages were explained by the fat metabolism of the ruminants. CONCLUSION: Organic winter milk is low in several desirable FAs. Diets rich in mature fodder and sugar were a poor choice for an improved FA composition. c  2011 Society of Chemical Industry Keywords: fatty acids; cow’s milk; organic; winter fodder INTRODUCTION The milk fatty acid (FA) composition of cow’s milk is very different between the grazing season when cows have access to fresh grass and winter diets that are based on forages, like hay, grass silage, legume silage and maize silage. 1,2 Changes differ depending on the subgroups of FAs, and it has been shown that several isomers of conjugated linoleic acid (CLA) like cis-9, trans-11 (c9t11) and cis-11, trans-13 (c11t13) are indicators of grazing management. 3 Going from grass-based summer feeding towards winter feeding based on dried or ensiled fodders, the milk fat consistency and fat colour change. The level of carotenes drops in winter milk and the reduction of long-chain polyunsaturated fatty acids (LC-PUFA) leads to pale butter and pale cheeses with a more crumbling structure, called ‘short’, instead of the supple, flexible character of the summer cheese. Couvreur et al. 4 used the ‘spreadability index’, C16 : 0/C18 : 1 to describe changes in fat consistency and the melting point of butter fat. Winter milk contains fat with a higher degree of saturation, resulting in a poorer spreadability. The management at organic farms is mentioned as one of the factors for an improved FA composition. However, ‘organic’ as an explanatory factor has been criticized 5 and effects of ‘being organic’ depend, among others, on the interpretation of organic regulation, the intensification level of the farm as well as the season of sampling. Especially in summer, differences between organic and conventional milk have been traced back to the access to pasture and overall high fresh grass intake, and low levels of maize silage and concentrates in cows’ rations. 6,7 In winter diets, in Nordic regions as well as under intensified feeding with maize silage and concentrates, differences between conventional and organic farming are limited. 5,8 The quality of roughage, especially the amount of red clover in the silage, 9 also influenced the milk FA composition. The change of diet with regard to FA composition is limited within organic standards. The inclusion of oil seeds such as oil, toasted or crushed seeds is effective, the main focus being on rapeseed, sunflower and linseed oils as sources of: oleic, linoleic and linolenic acids. 10 Although it is known that feeding of oil seeds is a secure way to modulate FA composition, 1 oil seeds are expensive and it has been suggested that direct uptake of these seeds in the human diet would be more effective than feeding them to cows. In this article we investigated influences of different organic winter forages on milk FA composition. The goal is to understand the possibilities for improving cows’ organic winter diet. In the experimental diets the main focus is on changes in the roughage component, i.e. fodders that do not compete with direct human consumption. One possibility for improving the quality of roughage is to give attention to the quality of the harvesting process and origin of the hay. Conservation of grass in the traditional way is to field-dry in the summer months from a * Correspondence to: Ton Baars, Research Institute of Organic Agriculture (FIBL), Frick, Switzerland. E-mail: ton.baars@fibl.org † This paper reflects the oral presentation at the International Conference Organic Food Quality and Health, Prague, 18 – 20 May 2011. a Department for Biodynamic Agriculture, University of Kassel, 37213 Witzen- hausen, Germany b Department of Nutritional Physiology, Institute of Nutrition, Friedrich Schiller University of Jena, 07743 Jena, Germany c Current address: Research Institute of Organic Agriculture (FIBL), 5070 Frick, Switzerland J Sci Food Agric (2012) www.soci.org c  2011 Society of Chemical Industry