Increasing the oleic acid (18:1 cis-9) content of milk fat might be desirable to meet consumer concerns about dietary healthfulness and for certain manufacturing applications. The extent to which milk fat could be enriched with oleic acid is not known. Increasing the intestinal supply of polyunsaturated fatty acids decreases dry matter intake (DMI) in cows, but the effects of oleic acid have not been quantified. In a crossover design, 4 multiparous Holstein cows were abomasally infused with increasing amounts (0, 250, 500, 750, or 1,000 g/d) of free fatty acids from high-oleic sunflower oil (HOSFA) or with carrier alone. Continuous infusions (20 to 22 h/d) were for 7 d at each amount. Infusions were homogenates of HOSFA with 240 g/d of meat solubles and 11.2 g/d of Tween 80; controls received carrier only. The HOSFA contained (by wt) 2.4% 16:0, 1.8% 18:0, 91.4% 18:1 cis-9, and 2.4% 18:2. The DMI decreased linearly (range 22.0 to 5.8 kg/d) as the infused amount of HOSFA increased. Apparent total tract digestibilities of dry matter, organic matter, neutral detergent fiber, and energy decreased as the infusion increased to 750 g/d and then increased when 1,000 g/d was infused. Digestibility of total fatty acids increased linearly as infused fatty acids increased. Yields of milk, fat, true protein, casein, and total solids decreased quadratically as infused amounts increased;

Modification of milk fat composition might be desirable to alter manufacturing characteristics or produce low saturated fat dairy products that more closely meet consumer dietary preferences. The aim of this research was to evaluate functional properties of butter oil obtained from milks with fat composition modified by altering the profile of long-chain fatty acids (FA) absorbed from the small intestine of cows. A control and 5 mixtures of long-chain free FA were infused into the abomasum of lactating dairy cows in a 6 x 6 Latin square design with 21-d periods. Treatments were 1) control (no FA infused), 2) mostly saturated FA (C16:C18 = 0.72), 3) low-linoleic palm FA (C16:C18 = 0.85), 4) palm FA (C16:C18 = 0.72), 5) soy FA (C16:C18 = 0.10), and 6) high-palmitic soy FA (C16:C18 = 0.68). All treatments included meat solubles and Tween 80 as emulsifiers. Solid fat content (from 0 to 40 degrees C), melting point, and force at fracture were determined in butter oil. Milk fat from cows infused with palm FA (treatment 4) exhibited functionality equal to or better than control butter oil. Infusion with palm FA increased amounts of triglyceride (TG) fractions with 48, 52, and 54 carbon numbers but decreased TG with 32, 34, 36, and 42 carbon numbers. Infusion with soy FA increased TG with 26, 38, 40, 52, and 54 carbon numbers but decreased TG with 34, 42, and 46 carbons. Infusion of the mostly saturated FA increased TG with 38, 50, 52, and 54 carbon numbers but decreased TG with 32, 34, and 42 carbon numbers. These TG groups were consistently correlated with functional properties of butter oils from different treatments. The content of palmitic acid is important for maintaining functionality in the presence of increased polyunsaturated FA. The composition of milk fat may be able to be optimized through nutritional manipulation of diets for dairy cows if the optimal composition of FA and TG is defined for a particular dairy product.