Dairy cows have increased energy demands during the transition period that are not met by the diet, causing negative energy balance.

Cows adapt to energy deficits by mobilizing body fat reserves from adipose tissues through a process known as lipid mobilization. Although this is a physiological adjustment common among mammals, lipid mobilization is exacerbated in the dairy cow with the genetic drive for high milk production, resulting in elevated concentrations of blood lipids, especially non-esterified fatty acids (NEFA), says Andres Contreras, Ph.D. candidate at Michigan State University.

The direct outcome of lipid mobilization is the rise in NEFA concentrations, and NEFA levels have an impact on immune function. Research also indicates that there are changes in both composition and concentration of NEFA levels that may have consequences to cow health. The importance of controlling lipid metabolism has long been recognized in modifying the outcome of human diseases, says Contreras. Changes in the human diet that alter and reduce fat mobilization have contributed enormously to public health. A greater understanding of fatty acid dynamics during the exaggerated fat mobilization events in transition dairy cows may also prove to be successful in reducing disease susceptibility. Supplementing specific fatty acids, coupled with strategic feeding, may enable a more robust immune system during the transition period.

Lipid science is still in its infancy, but the perceived role of fat as simply a dormant energy store is now defunct and a lot remains to be learned about how lipids influence life.