The role of fatty acids in the regulation of milk fat synthesis

Experiments were performed to further investigate the impact of supplemental fatty acids on lipid metabolism in lactating cows and rats. Feeding supplemental fat to lactating dairy cows to increase the energy density of the diet has been a method to increase milk production. Saturated fats such as palmitic acid, can be fed at a higher rate than unsaturated fatty acids before inhibiting dry matter intake (DMI). DMI increased when 500 g of fatty acids of palm were fed to lactating cows but feeding higher levels did not alter DMI when compared with controls. Both milk production and DMI were maximized when 500 g of fatty acids of palm was fed while milk fat production increased linearly as the concentration of fat in the diet increased. Under some feeding regimes such as low fiber and high polyunsaturated fatty acids, milk fat production can be drastically reduced. This milk fat depression (MFD) results from altered ruminal biohydrogenation of fatty acids resulting in the production of unique fatty acids, such as t10, c12 CLA. In lactating rats we observed a decrease in milk fat percentage in restricted fed but not ad libitum fed dams. There were also no differences in growth rates of litters nursing dams supplemented with t10, c12 CLA. The rat liver was strongly affected by t10, c12 CLA supplementation resulting in increased expression of genes associated with beta-oxidation, ketone body metabolism and cholesterol metabolism. The mammary gland of lactating rats was more strongly affected by food restriction resulting in decreased expression of several genes associated with fatty acid synthesis. In lactating cows MFD was induced by infusion of t10, c12 CLA, however, the microarray analysis used was unable to identify changes in genes typically decreased in the mammary gland during MFD. A consistent decrease in genes associated with beta-oxidation, which might partially contribute to MFD was detected. Although the rat liver data is consistent with published data, the mammary gland will require further investigation to establish the mechanism in which t10, c12 CLA induces MFD. Further investigation is required to evaluate gene expression changes in response to fatty acid supplementation.