Feed composition and strategies to improve poly-unsaturated fatty acid levels in organic cow milk

Summary

Like in various other countries, organic milk in the Netherlands has higher levels of poly-unsaturated fatty acids, particularly CLA and omega-3, than conventional milk. Monitoring results from a total of 25 farms between 2004 till 2007 are presented. Regression analysis indicates a negative effect of maize silage and positive effects of feeding fresh grass, grass pellets, red clover and addition of oil on CLA levels in milk fat. Results with omega-3 are similar, but omega-3 levels in milk fat seem less related to feed characteristics: the model with feed composition, seasonal effects and farm effects as major parameters, explains a smaller part of the variation, while farm influence is much larger with omega-3 compared to CLA.
Farm influence might be caused by genetic differences and constant factors influencing roughage quality. Genetic influences are likely but could not be investigated as milk samples were not taken from individual cows. The influence of grass quality is suggested by the large effect of sampling date found in this study. Moreover, some high residual values and statistical estimates for individual farms seem often related to silage quality, botanically rich pastures and red clover feeding.