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

Our experiment was carried out with Holstein cows in midlactation to assess effects of feeding 0 or 40 g formalintreated canola oil as htec@' in combination with 0 or 400 IU of vitamin IYkg 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 C1g-rich untreated oil, i.e., a marked increase in the proportion of stearic, oleic, linoleic and linolenic acids and a concomitant decrease in c 6 to c 1 6 fatty acids. High vitamin E diet increased vitamin E content in milk fat to 40 to 50 pg/g, i.e., similar to that reported for cows on pasture. There was no significant dietary F' rotec@ x dietary vitamin E interaction. Measurement of thiobarbituricacid-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 Cute by milk proteins. It was established that the unsaturated fatty acids of canola oil in Rote@ were not well protected from hydrogenation in rumen and that thiobarbituric acid data shodd be intexpreted with caution.