[Mechanisms of the lactogenic action of thyroid hormones and nonspecific resistance in ruminants].

Abstract

Studied was the effect of thyroid hormones on the nonspecific resistance and the milk productivity of ruminant animals in the conditions of hypodynamia and in various functional conditions of the thyroid gland. Both the removal of the thyroid gland (thyroidectomy) and the hypofunction of the gland (as induced by ammonium perchlorate at 10 mg/kg body mass) were accompanied by the drop of the indices characterizing the nonspecific resistance of the animals as well as their milk productivity. The immobilization of lactating ruminant animals (hypodynamia) had a negative impact on the milk producing process, enhanced the incretion of ACTH, lowered the release of thyroid hormones (T3, T4, FT4) and decreased milk productivity, deteriorating the biologic properties of colostrum. The thyroid gland and its hormones (T4, T3) were shown to have a positive effect on milk secretion, raising the activity of the enzyme adenylate cyclase and the amount of the cyclic 3.5 cyclic adenosine monophosphate (cAMP) in the parenchymal tissue of the mammary gland.