Milk yield and composition during abomasal infusion of conjugated linoleic acids in dairy cows.

Conjugated linoleic acids refer to a mixture of positional and geometric isomers of linoleic acid with conjugated double bounds. Three supplements of conjugated linoleic acids which differed in isomer enrichment were infused into the abomasum of lactating dairy cows to determine postruminal effect on milk yield and composition. Four Holstein cows were used in a 4 x 4 Latin square design. Treatments were 3-d abomasal infusion of 1) control, 5 kg of skim milk (carrier for conjugated linoleic acid supplements), 2) conjugated linoleic acid supplement 1 (28.8 g/d; 6.9 g of cis/trans 9,11; 6.4 g of cis/trans 8,10), 3) conjugated linoleic acid supplement 2 (48.5 g/d; 7.1 g of cis/trans 9,11; 4.1 g of cis/trans 8,10; 8.3 g of cis/trans 10,12; 5.5 g of cis/trans 11,13), and 4) conjugated linoleic acid supplement 3 (16.3 g/d; 7.1 g of cis/trans 9,11; 7.2 g of cis/trans 10,12). Infusions increased the conjugated linoleic acids content of milk fat from 0.43 g/100 g of fat for the control treatment to 1.02, 1.52, and 0.95 g/100 g of fat for conjugated linoleic acid supplements 1, 2, and 3, respectively. Apparent efficiency of transfer in milk fat was 25.2, 33.5, 21.0, and 28.4% for cis/trans 8,10, cis/trans 9,11, cis/trans 10,12, and cis/trans 11,13, respectively. Infusion of conjugated linoleic acids had no effect on dry matter intake, milk yield, and milk protein content. However, conjugated linoleic acid supplements reduced the content and yield of milk fat by 28 and 25%, respectively. The similarity of response for the different conjugated linoleic acid supplements did not allow us to identify the specific role of different isomers, but the changes in milk fatty acid composition indicated that effects were primarily on de novo fatty acid synthesis and the desaturation process.