Question

557 164 Grad student Kristine Flaherty fed a high-fat diet to lactating dairy cows. She measured the net uptakes of blood metabolites by the mammary glands and the production of milk components: low-fat high-fat mammary uptakes, mmol/h glucose 509 acetate 1480 1592 long-chain fatty acids 101 (NEFA + TAG) yields in milk, kg/d milk 34.9 37.2 lactose 1.66 1.80 fat 1.27 1.43 short-chain FA (C4 - C14) 0.46 long-chain FA (C16 - C18) 0.66 0.97 protein 1.14 1.15 0.61 From what you know of lipogenic tissues, give a metabolic explanation of how the high-fat diet caused

a) the increase in long-chain fatty acid yield

b) the decrease in short-chain fatty acid yield

c) the increase in lactose yield

d) the increase in milk yield

Answer 1

Solution:

a) High-fat diet increase in long-chain fatty acid yield

There is mainly three types of fat dominant in milk, short, intermediate or long-chain fatty acids, in which the short-chain acids are synthesized within the mammary gland from acetate and beta-hydroxybutyrate; long-chain acids are almost exclusively derived from blood plasma fatty acids of dietary origin; and intermediate-chain acids arise from both sources. In short, about 50 percent of the fatty acids in milk are synthesized in the mammary gland and the other 50 percent are derived directly from blood. Fatty acids are synthesized in the mammary gland via the malonyl coenzyme A (malonyl-CoA) pathway. Blood beta-hydroxybutyrate is primarily used for the first four carbons initiating fatty acid synthesis.

Hence, from the table above in the question, it is clear that feeding of high-fat diet increase the long-chain fatty acid in cow milk.

b) High-fat diet decrease in short-chain fatty acid yield

As explain in above paragraphs, high fat diet improve the synthesis of long-chain fatty acid in the mammary gland of cows, however, the short-chain acids are synthesized within the mammary gland from acetate and beta-hydroxybutyrate. Hence, no effect of the high fat diet on the short-chain fatty acid.

c) & d) High-fat diet increase in lactose as well as milk yield

Feeding dairy cows with high-fat feeds could enhance their energy balance status by increasing the dietary energy density without increasing the dietary starch content. Consequently, supplemental fat in the diet could improve milk yield (MY) along with lacotse in particular during early lactation when energy supply does not meet the requirements for maintenance and production.

Conclusion

When lactating cows feeding on high-fat diet, its gene expression changed due to presence of high fat, subsequently, improve in lacose stsnthesis, milk production with improved quantity of long-chain fatty acid.