Changes of serum enzyme activities in cows with milk fat depression.

Serum activities of sorbitol dehydrogenase (SDH), lactate dehydrogenase (LDH), gamma-glutamyltranspeptidase (gamma-GT), and alkaline phosphatase (ALP) were measured before, during, and after milk fat depression in 9 cows fed a high-concentrate ration during 2 experiments. In 7 of the 9 cows, increases in serum SDH and LDH activities were observed during milk fat depression. The gamma-GT activity showed only moderate changes, whereas the ALP activity remained unchanged. During recovery from milk fat depression, decreases of SDH, LDH, and gamma-GT activities were found in nearly all cows. Association of this phenomenon with changes found in beef cattle, such as ruminal lesions and liver abscesses, are discussed.