Supplementing total mixed rations with pasture increase the content of conjugated linoleic acid in milk

Forty-five Holsteins cows in early to mid-lactation were used to evaluate the milk fatty acid composition of three feeding systems that combined pasture and total mixed ration (TMR) in a 19-week experiment. The three treatments were: (1) pasture plus concentrate (PC), (2) pasture plus TMR (PTMR), and (3) TMR. The content of short- and medium-chain fatty acids (FA) decreased from 11.3 to 9.0 g/100 g of FA and from 40.5 to 36.5 g/100 g, respectively, from the TMR to the PC treatment. The content of long-chain FA increased from 47.7 to 53.8 g/100 g as the amount of pasture dry matter (DM) intake increased from the TMR to the PC treatment. The content of saturated FA was lower (55.5 g/100 g versus 60.1 g/100 g) and the content of unsaturated FA was higher (43.9 g/100 g versus 38.6 g/100 g) in the PC treatment versus the PTMR and TMR treatments. As the amount of pasture DM intake increased from the TMR to the PC treatment, the content of conjugated linoleic acid (CLA) increased from 0.59 to 1.21 g/100 g, resulting in a 42 and 105% increase for the PC treatment compared to the PTMR and TMR treatments, respectively. The increase in CLA content in milk with inclusion of pasture was primarily associated with a higher intake of C18:3 and a higher delivery of trans11 C18:1 to the mammary gland.