Experimental improvement of cow milk fatty acid composition in organic winter diets.

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. 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. 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.