Milk Fatty Acid Composition and Mammary Lipid Metabolism in Holstein Cows Fed Protected or Unprotected Canola Seeds

摘要

Six midlactation Holstein cows were fed a total mixed ration supplemented with either 4.8/100 canola meal, 3.3/100 unprotected canola seeds plus 1.5/100 canola meal, or 4.8/100 formaldehyde-protected canola seeds, according to a double 3 x 3 Latin square design. Each period lasted 3 wk; experimental analyses were restricted to the last week of each period. Mammary biopsies were taken the last day of each period for gene expression measure- ments. Milk production and milk protein percentage were reduced by canola seeds, whether protected or unprotected. Protected canola seeds also decreased dry matter intake. Feeding canola seeds reduced the con- tent of C8 to C16 fatty acids in milk and increased the content of oleic acid (C_18:1c9). Unprotected canola seeds 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. Similar results were obtained for plasma fatty acids, with some specific features, such as an increased C_16:0/C_16:1, ratio with protected canola seeds. Canola seeds had no significant effects on insulin, triglycerides, or cholesterol present in serum, but in- creased the concentration of nonesterified fatty acids; a greater increase was obtained with protected canola seeds. Expression levels of acetyl-CoA carboxylase and delta 9-stearoyl-CoA desaturase genes measured in the mammary gland did not differ significantly betWeen diets. Therefore, the reduced C_18:0/C_18:1c9 ratio observed in milk with protected canola seeds was not due to an enhanced expression of the delta-9 desaturase in the mammary gland.