Supplementing different ratios of short- and medium-chain fatty acids to long-chain fatty acids in dairy cows: changes of milk fat production and milk fatty acids composition.

Milk fat synthesis might be promoted by the dietary addition of long-chain fatty acids (LCFA) or short- and medium-chain fatty acids (SMCFA). This study evaluated unprotected lipid supplementation with different ratios of SMCFA to LCFA, which had equivalent fatty acid (FA) proportions (by weight) to those in milk, on milk fat production and milk FA composition. Thirty-six Holstein cows (183±46 d in milk) were divided into 3 treatments according to a randomized block design. Cows in 3 treatments received supplements of 80 g/d of SMCFA mixture and 320 g/d of LCFA mixture (ratio of SMCFA to LCFA was 20:80); 400 g/d of butterfat (ratio of SMCFA to LCFA was 40:60); or 240 g/d of SMCFA mixture and 160 g/d of LCFA mixture (ratio of SMCFA to LCFA was 60:40). The FA compositions of the SMCFA mixture and the LCFA mixture were similar to the de novo synthesized FA (except C4:0) and preformed FA (except trans FA) found in the butterfat, respectively. Fatty acid supplements and butterfat were consumed by cows daily before the morning feeding during the 8-wk experimental period. Dry matter intake and milk yield were not different among the treatments. The milk fat percentage and total SMCFA concentration in milk fat tended to increase linearly and the proportion of milk total solids increased linearly with increasing ratios of SMCFA to LCFA in the supplements, whereas milk fat yield was not changed. We suggest that increasing ratios of SMCFA to LCFA in diets has the potential to improve milk fat synthesis.