EFFECTS OF FEEDING PROTEC AND ALPHA-TOCOPHEROL ON FATTY-ACID COMPOSITION AND OXIDATIVE STABILITY OF COWS MILK

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(R) 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 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 mu-g/g, i.e., similar to that reported for cows on pasture. There was no significant dietary Protec(R) x dietary vitamin E interaction. Measurement of thiobarbituric-acid-reactive substances showed that milk of cows fed high vitamin E was stable at 5-degrees-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(R) were not well protected from hydrogenation in rumen and that thiobarbituric acid data should be interpreted with caution.