Effects of Feeding Oleic Acid or Hydrogenated Vegetable Oils to Lactating Cows

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Abstract
Feeding trials were performed to clarify the mechanism by which unsaturated oil depresses milk fat percentage. Oleic acid at 250 or 500 ml/cow per day did not reduce milk fat percentage significantly. At 500 ml these changes were significant (control, oleic); rumen acetate 61.6, 60.3%; rumen propionate 19.4, 21.0%; milk fat content of 18:1 trans fatty acid 3.0, 8.0%; 18:2 cis fatty acid 2.2, 1.4%. Feeding hydrogenated vegetable oil containing 13% trans acid at 454 g/cow per day slightly decreased milk fat percentage and elevated plasma cholesterol 190-245 mg/100 ml and 18:1 trans fatty acid in milk fat 4.2-6.2%. Hydrogenated vegetable oil containing 49% 18:1 trans acid at 454 g daily decreased milk fat 3.9-3.1%. Milk fat triglycerides decreased in short chain fatty acids and increased in 18:1 trans 2.6-11.2%, 18:1 cis 22.9-29.0% and 18:2 trans 0.2-1.8%. Milk phospholipids decreased 14.1-9.6% in 14:0 fatty acid and increased 0.3-3.1% in 18:1 trans and 20.5-31.4% in 18:1 cis. Blood cholesterol esters were increased 152-195 mg/100 ml. trans acids or compounds produced in the rumen during their formation from polyunsaturated fatty acids are responsible for milk fat depression from unsaturated oils.