Seasonal changes of CLA isomers and other fatty acids of milk fat from grazing dairy herds in the Azores

BACKGROUND: Season of the year associated with dietary changes has been recognized as a factor implicated in milk fat fatty acid (FA) profile in dairy cows. However, a lack of information exists concerning cows grazing all year round as is practiced in the Azores, where cows are supplemented in winter with maize silage plus concentrates, while in spring the higher grass allowance only requires supplementation with concentrate. The main objective of this study was to detect any seasonal variation of FA profile of milk fat from milk sampled in bulk tanks of 12 Azorean dairy herds. RESULTS Compared to winter milk, milk fat from spring presented a higher proportion of CLA cis ‐9, trans ‐11 (14.3 versus 9.6 g kg −1 FA), C18:1 trans ‐11 (32 versus 22 g kg −1 FA), C18:2 trans ‐11, cis ‐15 (3.7 versus 2.2 g kg −1 FA), CLA trans ‐11, cis ‐13 (0.34 versus 0.23 g kg −1 FA) and C18:3 n‐3 (5.7 versus 5.4 g kg −1 FA). The C18:2 n‐6/C18:3 n‐3 ratio was lower ( P < 0.05) in spring. Branched‐chain FA, except the anteiso ‐C15:0, were higher in spring, while odd‐chain FA (C15:0) were higher in winter. CONCLUSION: Dairy herd management in the Azores presents a seasonal variation of milk fat FA composition, where the spring milk may present increased potential benefits for human consumers.