Effects of vitamin E and flaxseed on rumen-derived fatty acid intermediates in beef intramuscular fat

To elucidate the effects of dietary vitamin E with or without flaxseed on beef fatty acid composition, 80 feedlot steers were fed 4 diets: Control-E (451 IU dl-α-tocopheryl acetate/head/day), Control + E (1051 IU dl-α-tocopheryl acetate/head/day), Flax-E (10% ground) and Flax + E. Vitamin E had no effect on animal growth or carcass weight (p > 0.05), while flaxseed-fed steers had greater average daily gain (p = 0.007), final live weight (p = 0.005) and heavier carcasses (p = 0.012). Feeding flaxseed increased the total n−3 fatty acid content of beef and this response was further accentuated by the inclusion of high levels of vitamin E in the diet. Feeding flax increased levels of some 18:3n−3 partial hydrogenation products including c15- and t13/14-18:1 and several 18:2 isomers (p < 0.001) but decreased t10-18:1 (p < 0.001). Vitamin E enhanced intramuscular levels of 18:3n−3 and its biohydrogenation products leading to greater accumulations of total n−3 fatty acids in lean ground beef. The consequences of increasing the concentrations of partially hydrogenated products on human health have yet to be investigated.