[Growth in weaned piglets and levels of iodothyronines in the blood during the administration of thyroactive substances].

In five trials with 100 piglets we studied the effects of thyreoglobulin, potassium nitrite and the thyreostatic preparation Carbimazol, which were added to a complete starter in the period from early weaning to the age of four weeks. Changes in the concentrations of thyroxine (T4) and triiodothyronine (T3) in the blood serum of control unmedicated piglets weaned from the sows can be characterized, after a short rise, by a decrease which stopped usually in the fourth week, accompanied by higher body weight gains. The lowest drop of T4 level was recorded in the group given potassium nitrite, with 21% methemoglobin, having the highest actual and relative weight gains. The T4 and T3 levels were not influenced by thyreoglobulin. They were decreased by Carbimazol by more than two thirds of the values which were usual at weaning if Carbimazol was administered at the highest rate of 60 mg per 1 kg of feed; neither was the growth of body weight nor feed consumption per unit of weight gain negatively influenced. An application of thyreotropic hormone on the 14th day after weaning demonstrated an inhibition of iodothyronine secretion in piglets which had been given Carbimazol, and a good response in control piglets. We drew a conclusion that the decrease in T4 and T3 levels after early weaning did not occur when iodothyronine intake with mother milk was interrupted nor was it caused by iodine deficiency, nor was it a primary cause of the reduced growth rate of piglets.