The effects of saturated fatty acid supplements on plasma and milk concentration of fatty acid esters of hydroxy fatty acids in dairy cows.

Fatty acid esters of hydroxy fatty acids (FAHFA) are a novel class of bioactive lipids with demonstrated antidiabetic and anti-inflammatory properties in rodent models and humans but have not been investigated in cows. The major FAHFA are synthesized from palmitic (PA), stearic (SA), and oleic acid. The PA can be esterified to hydroxy fatty acids, such as hydroxy PA or hydroxy SA, or SA can be esterified to hydroxy SA, forming PAHPA, PAHSA, or SAHSA, respectively. The objective of the current study was to determine the effect of increasing intake of PA, SA, or both PA and SA on nonesterified FAHFA in the plasma and milk of dairy cows. We hypothesized that increasing PA and SA in the diet would increase PA and SA containing FAHFA in plasma and milk. Samples were analyzed from a previous experiment that used 12 multiparous Holstein cows in a 4 × 4 Latin square design. Treatments were a no-fat supplement control (CON) and fat supplements that were high in PA (91% C16:0), high in SA (92.6% C18:0), or contained a blend of PA and SA (PA/SA; 45.3% C16:0 and 49.1% C18:0) at 1.95% of diet DM. The concentrations of nonesterified FAHFA in plasma and milk fat were quantified using liquid chromatography tandem MS, and data were analyzed using a mixed model that included treatment as a fixed effect and cow and period as random effects. The relationship between plasma FAHFA and milk production variables were analyzed using regression analysis. Five nonesterified FAHFA (9-PAHPA, 5-PAHSA, 9-PAHSA, 10-PAHSA, and 9-SAHSA) were quantified in plasma and all were affected by treatment. Plasma concentration of 9-PAHPA was increased 2.9-fold by PA compared with CON, whereas 9-SAHSA was increased 2.7-fold by SA compared with CON. The concentrations of 5-PAHSA, 9-PAHSA, and 10-PAHSA were highest with PA/SA. In milk, 8 nonesterified FAHFA were quantified, and only 12-PAHSA was increased by SA and 12-PAHPA tended to be increased by PA. Plasma 9-PAHPA was positively associated with milk fat yield and mixed FA and negatively associated with milk preformed FA, de novo FA, and odd- and branched-chain fatty acids, whereas plasma 9-SAHSA was positively associated with milk preformed FA. Overall, FA supplements affected nonesterified FAHFA concentration in plasma, demonstrating a direct effect of dietary FA on this emerging regulator of metabolism. There were limited effects of FA supplements on nonesterified FAHFA in milk fat. Functional roles for these lipids require further exploration.