Milk production and milk fatty acids in dairy cows fed crushed rapeseed or rapeseed oil

•Dairy cow diets were supplemented with full fat crushed rapeseed or its free oil.•Rapeseed fat supplementation increased daily dry matter intake and milk yield.•Rapeseed fat increased content of long chain and unsaturated fatty acids in milk fat.•Fatty acids of crushed rapeseed are partly protected against ruminal hydrogenation.

The effect of crushed full fat rapeseed or its free oil on milk yield and milk fatty acid composition was assed using three groups of mid-lactating Holstein dairy cows, assigned to a randomized 3×3 Latin square design. Dietary treatments included a control (CTL, ether extract 2.3% of dry matter, DM) and two experimental treatments (ether extract 4.2% of DM) supplemented with the same amount of fat either supplied as 4.9% of DM crushed full fat rapeseed, RCor2.2% of DM free rapeseed oil RO. Both experimental treatments increased DM intake (P<0.005) and daily milk yield (P<0.001). Milk fat and protein concentration was decreased in the supplemented diets (p<0.001). A reduced (p<0.001) yield of saturated fatty acids (FA) and an increased yield of long chain and unsaturated FA (p<0.001 for mono unsaturated FA and p<0.05 for poly unsaturated FA) in milk fat was observed for both experimental treatments. The results confirmed a reduced de novo synthesis and an increased carry-over of dietary FA upon feeding dairy cow diets supplemented with long chain and unsaturated FA. The lower degree of saturation in milk fat from cows fed RC compared to RO indicates a partial protection of the crushed rapeseed against ruminal hydrogenation.