Herb feeding increases n−3 and n−6 fatty acids in cow milk

Most work dealing with the impact of species-rich herbage on milk fatty acid content has hitherto been carried out in alpine areas or semi-natural grasslands. The main objective of the present study was to examine the effect of herbs sown and intensively managed in a lowland sward on the concentration of n−3 and n−6 fatty acids and vitamins in cows' milk compared to clover grass and total mixed ration (TMR) feeding. Twelve cows were housed in tie-stall and randomly allocated to three diets fed ad libitum for 14 days: HERBS (mixture of fresh herbs); CLOVER (mixture of fresh white clover and ryegrass); or TMR (total mixed ration based on silage and concentrate). n−3 fatty acid (FA) content was similar between the three diets, while n−6 FA content was highest in the TMR diet. A twofold increase in n−3 FA concentration in milk was observed when feeding HERBS compared to CLOVER and TMR (0.8, 0.4 and 0.3 g/kg milk, respectively). n−6 FA concentration increased as well when feeding HERBS (1.4, 0.9 and 1.0 g/kg milk for HERBS, CLOVER and TMR, respectively). Transfer efficiency from feed to milk was doubled for n−3 FA when feeding HERBS and for transfer efficiency of n−6 FA from feed to milk an increase of 28% was observed for HERBS compared to CLOVER. Retinol content was highest in HERBS milk, while there was no difference in α-tocopherol and ß-carotene milk content between the three diets. The results thus support previous findings on the effect of herbs on the milk fatty acid profile, but it will require further research to understand the effect of herbs on n−3 and n−6 FA concentration in milk. In conclusion, milk content of polyunsaturated fatty acids (PUFA), like n−3 and n−6 FA, was significantly increased when herbs constituted the major part of the herbage, despite lower or similar dietary content of n−3 and n−6 FA in herbs compared to clover grass- and TMR diets.