Milk yield and composition during abomasal infusion of conjugated linoleicacids in dairy cows

Conjugated linoleic acids refer to a mixture of positional and geometric is omers 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 o n 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 o f skim milk (carrier for conjugated linoleic acid supplements), 2) conjugat ed 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 conjug ated linoleic acid supplements 1, 2, and 3, respectively. Apparent efficien cy 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. Inf usion of conjugated linoleic acids had no effect on dry matter intake, milk yield, and milk protein content. However, conjugated linoleic acid supplem ents reduced the content and yield of milk fat by 28 and 25%, respectively. The similarity of response for the different conjugated linoleic acid supp lements did not allow us to identify the specific role of different isomers , but the changes in milk fatty acid composition indicated that effects wer e primarily on de novo fatty acid synthesis and the desaturation process.