Illini DairyNet Papers
During the past decade, Americans have become increasingly health conscious. Reports in the media have highlighted recommendations from the medical community and government agencies that people decrease their intake of saturated fatty acids because of the purported relationship of saturated fatty acids with atherosclerosis. In particular the saturated fatty acids myristic and palmitic acids may increase plasma cholesterol in humans; however, the saturated fatty acid stearic acid may not affect plasma cholesterol. Dairy products have been a target for human health advocates because milk fat contains about 70% saturated fatty acids, 25% monounsaturated fatty acids, and 5% polyunsaturated fatty acids. Over one-half of the saturated fatty acids in milk are myristic acid or pa1mitic acid.
In 1988, the Wisconsin Milk Marketing Board assembled a group of 15 researchers from industry and academia to discuss the potential future uses of milk fat. These researchers concluded that the "ideal" milk fat for use in the human diet would contain <10% polyunsaturated fatty acids, <8% saturated FA, and >82% monounsaturated fatty acids. Such a large change in the fatty acid composition of milk is not possible by alteration of the diet of dairy cows; however, there is potential to alter the fatty acid composition of milk to make it more compatible with the human diet.
Whole oilseeds (e.g. soybean, sunflower, and canola) contain primarily unsaturated fatty acids; however, most of the unsaturated fatty acids fed to cows are converted to saturated fatty acids by ruminal microorganisms. This results in primarily saturated fatty acids in milk fat despite consumption of a diet high in unsaturated fatty acids. Saturation of unsaturated fatty acid in the rumen can be prevented experimentally by infusing fatty acids directly into the abomasum (bypassing the rumen). The objective of this experiment was to determine the potential to increase the content of monounsaturated fatty acids in milk fat by infusing different amounts of two fatty acid mixtures rich in the monounsaturated fatty acid oleic acid (derived from high-oleic sunflower or canola).
MATERIALS AND METHODS
Four Holstein cows fitted with ruminal cannulas were used to evaluate the effects of infusing different amounts of two free fatty acid mixtures (canola and high-oleic sunflower) into the abomasum. The major fatty acids in the canola fatty acid mixture were 62.5% oleic acid (monounsaturated) and 24% linoleic acid (polyunsaturated). The high-oleic sunflower fatty acid mixture contained 86% oleic acid (monounsalurate ), and only small amounts of other fatty acids.
Two cows were continuously infused with each fatty acid mixture into the abomasum during each 21-day period. The fatty acid mixtures were infused for 3 days at each of four amounts in a sequence of 0, .3, .6, .9, .6, .3, and O pounds/day (a total of 21 days for each fatty acid mixture); cows then were changed to the opposite fatty acid mixture, and the infusion sequence was repeated. Milk samples were taken from two consecutive milkings every 3 days so that a sample was obtained during infusion of each amount of fatty acids. Fatty acid content of milk was determined.
Figure 1 shows the effect of fatty acid infusion on fatty acid composition of milk. Short- and medium-chain fatty acids and palmitic acid (saturated) in milk fat decreased similarly when increasing amounts of fatty acids from either high oleic sunflower or canola mixtures were infused. Short- and medium-chain saturated fatty acids are synthesized by the mammary gland and the infusion of free fatty acids into the abomasum inhibited normal fatty acid synthesis in the mammary gland, which effectively decreased the amount of saturated fatty acids in milk fat. The content of oleic acid (monounsaturated) in milk increased when increasing amounts of free fatty acids were infused into the abomasum. The increase was greater when the high-oleic sunflower fatty acid mixture were infused than when the canola fatty acid mixture was infused, the oleic acid content of the high-oleic sunflower fatty acid mixture was greater than the canola fatty acid mixture. The content of linoleic acid (polyunsaturated) in milk increased with abomasal infusion of increasing amounts of the canola fatty acid mixture, but not when increasing amounts of the high oleic sunflower fatty acid mixture was infused. This corresponds with the greater linoleic acid content of the canola fatty acid mixture compared with the high-oleic sunflower fatty acid mixture. Infusion of fatty acids from the high-oleic sunflower or canola mixtures effectively increased the content of unsaturated fatty acids in milk fat.
The fatty acid composition of milk can be altered by providing specific fatty acids to the abomasum of lactating dairy cows. Our data indicate that contents of short- and medium-chain fatty acids(including myristic and palmitic acids) decreased, and the content of oleic acid (monounsaturated) increased when .9 pounds/day of fatty acids from high-oleic sunflower or canola mixtures were infused into the abomasum. This indicates that the content of saturated fatty acids in milk fat can be decreased and the content of mono- and polyunsaturated fatty acids in milk fat can be increased by providing unsaturated fatty acids directly to the abomasum. Additional research will be necessary to determine whether increases in the oleic acid content of milk would be even greater if more oleic acid was provided into the abomasum. Likewise, development of technology that enables the protection of unsaturated fatty acids from saturation in the rumen will be necessary before the fatty acid composition of milk fat can be altered simply by feeding unsaturated fatty acids to lactating dairy cows.
Figure 1 may be viewed in PDF