Utilization of energy involves the metabolism of carbohydrates and lipids. Normally, carbohydrate metabolism dominates, but in states of negative energy balance, lipid metabolism becomes dominant.
Carbohydrate metabolism: This involves the production, breakdown and use of carbohydrates within organisms. The most important product of carbohydrate metabolism is glucose, the principal source of energy for cells. It is only when glucose is limiting that lipid metabolism takes over. Clinical assessment of carbohydrate metabolism involve blood glucose measurements and tests that approximate the duration and severity of glucose increases in the blood (fructosamine and glycosylated hemoglobin; note the latter is no longer used for this purpose and has largely been supplanted by fructosamine). Various hormones influence carbohydrate metabolism, notably insulin and corticosteroids.
Lipid metabolism: This involves the production, breakdown and use of lipids. The major source of lipid is exogenous through the diet and endogenous through breakdown of adipose tissue (lipolysis of fat). Various hormones influence lipid metabolism, such as lipoprotein lipase.
Lipid overview: Information on lipemia, lipoprotein classes and hormones involved in lipid metabolism.
Tests for carbohydrate metabolism
Glucose: This also includes the hormones that modulate glucose levels in blood.
Cholesterol concentration. This is routinely offered on chemistry panels in dogs and cats at Cornell University.
Non-esterified fatty acids (NEFA): This is a marker of lipolysis, which occurs under states of negative energy balance. This can be done on any animal as a test for lipolysis, but is especially important for assessing transition cows for excess negative energy balance, which has deleterious effects on the health, reproductive status and milk production of dairy cows. It is offered as part of our metabolic profile and transition cow energy profile in dairy cows immediately postpartum. It is also offered on our camelid liver panel to assess for risk of hepatic lipidosis in this species.
β-Hydroxybutyrate: This is a marker of lipolysis, with excess NEFA being converted to ketones. These can spill over into milk and urine (urinary ketone measurement can also be used to assess for states of clinical and subclinical ketosis). BHB can be measured in blood in any animal (not usually horses, since they have poorly developed ketogenic pathways), but is usually done in dairy cows in the postpartum period to evaluate for clinical and subclinical ketosis.
Transition dairy cow energy metabolite assessment: An important veterinary application for testing of energy metabolism is monitoring of dairy cows during the transition period from late pregnancy to early lactation. This section provides more information on this.