RESUMO
The feasibility of dietary strategies to increase oleic acid content of milk fat is unclear. Four Holstein cows were infused abomasally with free long-chain fatty acids from canola (62.5% C18:1) or high oleic sunflowers (86% C18:1). Each fatty acid mixture was infused for 3 d at 0, 133, 267, 400, 267, 133, and 0 g/d for a total of 21 d; cows then were changed to the opposite fatty acid mixture, and the infusion sequence was repeated. The DMI and percentages of casein and whey N in milk were decreased by infusion of fatty acids, but milk yield and percentages of fat and NPN in milk were increased. Contents of short- and medium-chain fatty acids and C16:0 in milk fat decreased, and contents of C18:1, C18:2, and C18:3 increased, as fatty acid infusion increased. Contents of C16:0 and C18:0 in plasma triglyceride were decreased, and content of C18:1 was increased, by increasing infusion of fatty acids. All changes reversed when the amount of fatty acid infused was decreased. Within the range of amounts of fatty acids infused, the relationship between yield of C18:1 in milk fat and the amount of C18:1 infused into the abomasum was linear, and transfer efficiency was 54.1%. Increased concentration and yield of C18:1 in milk were attributable mostly to the increased exogenous supply of C18:1.
