Corticosteroids in nocturnal blood plasma of cows in the field related to stage of lactation and plasma acetoacetate.

Two materials of nocturnal blood plasma samples, each representing more than 100 cows unselected with respect to health condition, showed acetoacetate variations within a wide range, overlapping with the range for animals with clinical ketosis. Within each of the two materials a statistically significant (P smaller than 0.001) negative correlation (r equal to minus 0.30) was obtained between plasma corticosteroids and log acetoacetate. The lowest corticosteroid and the highest acetoacetate averages were obtained for animals which were within the first month of the lactation cycle. With increasing time post-partum the two components varied inversely, a maximum in corticosteroids coinciding with a minimum in acetoacetate in cows which had calved 2 1/2 to 3 months before the date of sampling. At this stage the mean plasma sugar was about 10 per cent higher than in early lactation. The corticosteroid ranges for different levels of acetoacetate overlapped extensively. Still cows with acetoacetate smaller than or equal to 0.6 mg/100 ml gave significantly higher corticosteroid averages than the rest of the material. But in animals exceeding the 0.6 mg limit no relationship was found between the severity of the ketonaemia and the steroid level. Thus, no difference was obtained between cows with clinical ketosis and animals which were moderately ketonaemic. Some change in adrenal function may be associated with the development of ketonaemic conditions in cows. But no proof has been provided of a direct adrenal involvement in the transformation of a case of subclinical ketosis to the clinical stage.