Milk fatty acid composition and mammary lipid metabolism in Holstein cows fed protected or unprotected canola seeds

Six midlactation Holstein cows were fed a total mixed ration supplemented w ith either 4.8% canola meal, 3.3% unprotected canola seeds plus 1.5% canola meal, or 4.8% formaldehyde-protected canola seeds, according to a double 3 x 3 Latin square design. Each period lasted 3 wk; experimental analyses we re restricted to the last week of each period. Mammary biopsies were taken the last day of each period for gene expression measurements. Milk producti on and milk protein percentage were reduced by canola seeds, whether protec ted or unprotected. Protected canola seeds also decreased dry matter intake . Feeding canola seeds reduced the content of C-8 to C-16 fatty acids in mi lk and increased the content of oleic acid (C-18:1c9) Unprotected canola se eds elevated the concentrations of C-18:0 Protected canola seeds increased the C-18:2 and C-18:3 content, and reduced the C-18:0/C-18:1c9 ratio. Simil ar results were obtained for plasma fatty acids, with some specific feature s, such as an increased C-16:0/C-16:1 ratio with protected canola seeds. Ca nola seeds had no significant effects on insulin, triglycerides, or cholest erol present in serum, but increased the concentration of nonesterified fat ty acids; a greater increase was obtained with protected canola seeds. Expr ession levels of acetyl-CoA carboxylase and delta 9-stearoyl-CoA desaturase genes measured in the mammary gland did not differ significantly between d iets. Therefore, the reduced C-18:0/C-18:1c9 ratio observed in milk with pr otected canola seeds was not due to an enhanced expression of the delta-9 d esaturase in the mammary gland.