Effects of oilseed supplements on milk production and quality in dairy cows fed a hay-based diet

The influence of rapeseed (Brassica napus L.) and linseed (Linum usitatissimum L.) added to a dry forage basal diet of dairy cows on feed consumption, milk yield and composition and milk fatty acid (FA) profile was investigated. According to a latin square design, twelve cows (106 ± 52 DIM) were assigned to three experimental theses which received a hay-base diet (permanent meadow, grain-vitamin-mineral premix and cereal mix) supplemented with a mixture of: crushed barley (1.0 kg) and crushed maize (0.5 kg), Control (C) diet; full fat ground rapeseed (1.0 kg), crushed barley (1.0 kg) and crushed maize (0.5 kg), Rapeseed (R) diet; extruded linseed (1.2 kg), crushed barley (1.0 kg) and crushed maize (0.5 kg), Linseed (L) diet. Dietary treatment did not affect DM intake. As result of the high amount of dietary ether extract (3.2, 5.8 and 5.7% of DM, respectively, for C, R and L diet) R and L diet showed higher crude fat intake compared to C one. Despite the high intake of crude fat and all over of the polyunsaturated fraction, milk yield and milk composition resulted similar among treatments probably because of lipids sources were administrated as full fat (ground or extruded) oilseeds. Compared to C diet, R diet resulted in milk containing significantly lower saturated fatty acids (SFA) (66.9 vs 60.9% of total detected FA) and higher monounsaturated fatty acids (MUFA) (24.2 vs 30.6%) percentage, but had no effect on polyunsaturated fatty acids (PUFA). With respect to C diet, L diet also significantly reduced the content of SFA (66.9 vs 59.8%) and increased both MUFA (24.2 vs. 29.1%) and PUFA (4.1 vs 4.7%). Among single FA, dietary treatment influenced the level of C16:0, C18:0, C18:1 n-9, C18:3 n-3, even if the latter showed similar valued between C and R diets. Feeding these levels of whole oilseeds (about one kg per head) had not clear effects on milk vaccenic acid and conjugated linoleic acid (CLA) content. The inclusion of rapeseed in the diet significantly reduced the content of n-6 FA in the milk, whereas the diet supplemented with linseed significantly increased the content of n-3 FA. L diet led to a lower n-6/n-3 ratio, an intermediate value was observed for R diet. However, C16:0, C18:1 n-9 and the n-6/n-3 ratio showed a significant interaction between diet and trial period. The use of oilseed rich in unsaturated fatty acids (UFA) in lactating dairy cows fed with hay-based diet resulted in substantial changes in milk FA profile with no effects on productive performance. Considering the increase of PUFA and the reduction of n-6/n-3 ratio as a desirable enrichment of milk fat from a human health perspective, under our experimental condition feeding linseed seems to improve better the nutritional value of milk than rapeseed.