Conjugated linoleic acid (CLA) content of milk from cows offered diets rich in linoleic and linolenic acid

Two experiments were conducted to determine the conjugated linoleic acid (C LA) content of milk from cows offered diets rich in linoleic and linolenic acid. In experiment 1, 36 cows were assigned to a control and five treatmen t groups. Cows in the control group received a diet containing 51% forage a nd 49% grain on a dry matter basis. In the treatment group, grain was partl y replaced by either 18% raw cracked soybeans, 18% roasted cracked soybeans , 3.6% soybean oil, 2.2% linseed oil, or 4.4% linseed oil. Experimental die ts were fed for 5 wk. Average CLA contents in milk fat from wk 2 through 5 were 0.39% in control and 0.37, 0.77, 2.10, 1.58, and 1.63% of total fatty acids in the raw soybean, roasted soybeans, soybean oil, 2.2% linseed oil, and 4.4% linseed oil treatments, respectively. In experiment 2, 36 cows wer e assigned to a control and 5 treatment groups. Cows in the control group r eceived a diet containing 55% forage and 45% grain. In the treatment groups , grain was partly replaced by soybean oil at 0.5, 1.0, 2.0, 4.0, or by lin seed oil at 1.0% of the dietary dry matter. Experimental diets were fed for 5 wk. Average CLA contents in milk fat from wk 2 through 5 were 0.50% in c ontrol and 0.75, 0.76, 1.45, 2.08,and 0.73% of total fatty acids in 0.5, 1. 0, 2.0, 4.0 soybean oil and 1.0% linseed oil treatments, respectively. Diet s rich in linoleic or linolenic acid can increase CLA content of milk when dietary oil is accessible to the rumen microorganisms.