EFFECTS OF BUFFERS ON MILK FATTY-ACIDS AND MAMMARY ARTERIOVENOUS DIFFERENCES IN DAIRY-COWS FED CA SALTS OF FATTY-ACIDS

Ten Holstein cows in early lactation were used in a replicated 5 x 5 L atin square design to study the effects of MgO and three buffers added to diets containing Ca salts of canola oil fatty acids. Treatments we re 1) control (basal diet; no buffer), 2) 1.1% NaHCO3 plus 1.1% KHCO3, 3) 1.9% NaHCO3, 4) 0.5% MgO, and 5) 2.0% Na sesquicarbonate (percenta ge of dry matter). The control diet contained 53% grass silage, 43% co ncentrate, and 4% Ca salts. Body weight, intake, milk yield, and perce ntages of milk fat, protein, and lactose were unaffected by treatments . Buffers and MgO tended to increase triacylglycerol extraction by the mammary gland and changed the proportions of some fatty acids in milk . Arterial concentrations of acetate and triacylglycerol were correlat ed with their respective arteriovenous differences. Extraction by the mammary gland was high for acetate (approximate to 58.2%), triacylglyc erol (approximate to 47.3%), propionate (approximate to 34.6%), and gl ucose (approximate to 24.3%). Extraction of free fatty acids, phosphol ipids, or cholesterol was negligible. Mammary triacylglycerol arteriov enous difference tended to be higher when MgO was fed than when NaHCO3 was fed. Sodium sesquicarbonate, NaHCO3, and the blend of bicarbonate buffers increased C-18:2 in milk fat when compared with the control t reatment. The concentration of C18:2 in milk fat decreased when MgO wa s fed, but the ratio of cis-C-18:1 to trans-C-18:1 increased compared with effects of dietary NaHCO3. Medium-chain fatty acids in milk fat t ended to be higher with Na sesquicarbonate than with NaHCO3. Buffers a nd MgO modified the profiles of fatty acids in milk.