Effects of Feeding Protec® and α-Tocopherol on Fatty Acid Composition and Oxidative Stability of Cow's Milk

Abstract

Our experiment was carried out with Holstein cows in midlactation to assess effects of feeding 0 or 40 g formalin-treated canola oil as Protec® in combination with 0 or 400 IU of vitamin E/kg of DM on fatty acid composition of milk fat, vitamin E content, and oxidative stability of milk stored under refrigeration. The effect of treated canola oil on fatty acid composition of milk fat was typical of feeding a C18-rich untreated oil, i.e., a marked increase in the proportion of stearic, oleic, linoleic and linolenic acids and a concomitant decrease in C6 to C16 fatty acids. High vitamin E diet increased vitamin E content in milk fat to 40 to 50 μg/g, i.e., similar to that reported for cows on pasture. There was no significant dietary Protec® × dietary vitamin E interaction. Measurement of thiobarbituric-acid-reactive substances showed that milk of cows fed high vitamin E was stable at 5°C for 5 d under .1 ppm Cu++ contamination. At 1 ppm Cu++ contamination, storage time showed an inverse relationship to the apparent concentration of thiobarbituric-acid-reactive substances. This artifact arises from absorption of Cu++ by milk proteins. It was established that the unsaturated fatty acids of canola oil in Protec® were not well protected from hydrogenation in rumen and that thiobarbituric acid data should be interpreted with caution. © 1991, American Dairy Science Association. All rights reserved.