Discussion The present study tested the hypothesis that dicotyledonous forage plants affect milk FA composition of dairy cowsdifferently when fed in different phenological stages. This hypothesis was based on the expectation of a changing content ofdistinct plant compounds inhibiting ruminal biohydrogenation as reported for phenolic compounds (Cabiddu et al., 2010;Jayanegara et al., 2011) and in particular for tannins (Khiaosa-ard et al., 2009). In this respect it was anticipated that feedingflowering plants would lead to an elevated recovery of polyunsaturated fatty acids, especially ALA, in the milk fat of cows. Anexpected decrease in forage CP content taking place from Veg to Rep could have supported this trend additionally (Gersonet al., 1986). However, with none of the three flowering dicot species such an effect was found. Actually, there was a trendto the opposite, namely a decrease in milk fat ALA and LA concentrations with ongoing development of all experimentalforages. Also the FA profiles and the apparent FA recovery in milk fat could not be clearly related to phenolic contents of theplants. Possible causes for these results are discussed below.