Effect of diet on the fatty acid pattern of milk from dairy cows

Abstract

Twelve dairy cows 130 days in milk were sorted by milk production and body weight and assigned to three feeding regimens in a 3 x 3 Latin-square design, in order to study the effects of diet on milk fatty acid (FA) composition. The cows were fed a total mixed ration (TMR) consisting of corn silage (60%) and concentrate (40%) on dry matter basis, or grazed pasture, without (P) or with 5 kg·d-1 concentrate as a supplement (SP). Supplemented grazing dairy cows produced significantly more milk than the cows on the TMR and P diets (P < 0.05). The supplementation of grazing dairy cows with a low fat concentrate did not significantly affect the milk fat FA profile. The pasture diet, with a supplement or not, decreased the concentration of saturated FA (P < 0.05) and increased the concentration of unsaturated FA (P < 0.05), of milk fat as compared to the TMR diet. The reduction in medium-chain FA was offset in large part by increases in long-chain FA (mainly oleic acid). The concentrations of conjugated linoleic acid (CLA) (P < 0.05) and trans-vaccenic acid were higher (P < 0.05) in the milk fat from the grazing cows. The results showed substantial variation among individual cows within treatments on milk fat content of CLA. Significant correlations were found for individual cow's milk fat CLA content across diets. Overall, this study indicates that the concentration of CLA in milk fat is enhanced by the dietary intake of pasture and that moderate low fat concentrate supplementation of grazing dairy cows increases performance without compromising the FA profile of milk fat.