Elevation of conjugated cis-9,trans-11-octadecadienoic acid in bovine milkbecause of dietary supplementation

Cows on pasture were fed full fat soybeans (toasted, flaked, and pelleted) or ground full fat rapeseeds to investigate effects on cis-9, trans-11-octa decadienoic acid in milk. Three herds of 16 cows each that were on pasture were fed 3.1 kg/d of unmolassed beet pulp (control), 3.0 kg/d of rapeseed c oncentrate, or 3.1 kg/d of a soybean supplement. The concentration of cis-9 , trans-11-octadecadienoic acid in the milk of cows fed the rapeseed and so ybean supplements was significantly higher than in the milk of cows fed the control diet during the feeding trial. Over the trial, the cis-9, trans-11 -octadecadienoic acid concentration in the milk of individual cows varied f rom 6.8 to 25.7 mg/g of fat in the control herd, from 10.6 to 33.5 mg/g of fat in the herd fed the rapeseed concentrate, and from 8.8 to 30.5 mg/g of fat in the herd fed the soybean supplement. The concentration of cis-9, cis -12-octadecadienoic acid, the substrate for cis-9, trans-11-octadecadienoic acid synthesis in the rumen, was 4.9 g/100 g of fatty acid methyl esters i n the milk fat of cows fed the soybean supplement, 2.5 g/100 g of fatty aci d methyl esters in the milk fat of cows fed the rapeseed concentrate, and 2 .3 g/100 g of fatty acid methyl esters in the milk fat of the control cows. Milk yield and milk constituent yields were not affected by supplementatio n of either full fat soybeans or rapeseeds compared with controls, but milk protein concentration was significantly reduced by both oilseed supplement s.