Role of adrenocortical system in occurrence of ketosis in high-yield dairy cows

Abstract

From the very onset of lactation, the requirements of the mammary gland have an advantage over the requirements of other organic systems, even in the case of clinically exhibited ketosis. In hypoglycemic, ketotic cows, the mammary gland utilizes glucosis approximately in the same degree as the mammary gland of cows with normal glycemia. This indicates that the regulatory role of hormones can have primary importance in the earliest phase of lactation, when metabolic processes are on the very brink of a ketotic state. That is why it is believed that, in conditions of a great burdening of the metabolism, inadequate activity by the adrenocortical system presents one of the primary factors in the etiopathogenesis of ketosis in dairy cows. It is still an open issue whether hypof unction of the adrenal cortex is a direct cause of this disorder, or whether its activity is a consequence of insufficient stimulation by ACTH. In ketotic cows, average concentrations of cortisol have been established in ketotic cows, from 23.98 nmol/l in blood serum, and it is approximately the same as in healthy cows in the corresponding phase of lactation. However, the vast range of individual values largely makes it difficult to make a correct evaluation of the functional state of the adrenal cortex of ketotic cows. On the grounds of individual figures, in 26% diseased cows cortisol concentration in blood serum is from 1.38 to 16.55 nmol/l, in 37% it is from 16.55 to 27.59 nmol/l, and in 37 percent it is over 27.59 nmol/l. This indicates that cows with clinical symptoms of ketosis can be divided into those with low, medium, or high values of cortisol concentration in blood serum. Following the stimulation of the adrenal cortex with ACTH, the individual differences in serum cortisol concentration are considerably decreased. The ratio between the lowest and the highest values of cortisol concentration before the application of ACTH is 1:6, while it is only 1:1.5 four hours following application. After that, the values again take on the starting characteristics, and 24 hours after the application of ACTH they return to the starting values, and the ratio between the individual values is 1:8. It seems that the function of the adrenal cortex has been preserved in cows with clinical symptoms of ketosis and it is capable of reacting fully to stimulation with corticotropin. The cortisolemia values indicate, primarily, that there are big individual differences regarding the regulation of the degree of activity of the adrenal cortex, so that it is possible that, in the ketotic state, it is rather a case of uncoordinated activities of the adrenal cortex with the organism requirements imposed by the mammary gland, than that it is a matter of its hypofunction. .