Effects of fat supplementation on milk production and composition by dairy cows on pasture: a review

Eighteen experiments involving 25 comparisons were reviewed to describe the main effects of fat supplementation on milk production and composition with grazing dairy cows. Results were analyzed comparing the fat supplemented and the control groups without supplemental fat, and were segmented according to the stage of lactation (early- or mid-lactation) and the degree of saturation of the fat supplement (unsaturated or saturated). Fat supplements, both saturated and unsaturated, did not affect ruminal fiber digestion. Pasture and total dry matter intake were not consistently affected by fat supplementation. Milk and 4% fat-corrected milk production were increased by 0.97 and 1.05 kg/cow per day with fat supplementation. Milk response to fat supplementation was higher in mid-lactation cows and when saturated fat sources were fed. Milk fat concentration was increased 5.1% with saturated fat supplementation and decreased 8.0% with unsaturated fat supplementation when compared to control groups. Feeding unsaturated fats increased long-chain unsaturated fatty acids in milk fat including conjugated linoleic acid. Milk protein concentration was reduced by feeding unsaturated fat supplements, although milk protein yield was not affected. The experimental results reviewed suggest that fat supplementation to the diet of dairy cows grazing high-quality pastures generally increases milk production although the effects on milk composition depend on the degree of saturation of the fat supplement.