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

¹ Animal Research Center, Research Branch, Agriculture Canada, Ottawa, ON K1A 0C6, Canada

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® x 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.

Key Words: fatty acid • milk oxidation • -tocopherol

Submitted on February 23, 1990
Accepted on July 20, 1990

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