[The effect of carbamide feeding over a long period of time on thyroid gland activity in bulls].

In this experiment, 10 fattening bulls were given 0.27-0.42 g/kg body-weight of urea daily for 4 months. The bulls slaughtered after the experiments showed enlarged thyroid glands. These thyroid glands were much larger than the control glands (P = 0.1%). At the end of the experiment the bulls fed with urea weighed, on average, 44 kg more than the control bulls (P = 5%). The histology and electron-microscopy tests revealed that the bulls had hyperplasia of the thyrocytes, grave hydropic and vacuolar degeneration of the thyroid glands, and a considerable decrease in the colloids of the folliculus. The morphological test on the thyroid glands of bulls fed with the aforementioned level of urea daily for a longer period corresponded with the considerable alterations observed when treating bulls with thiouracil by-products. The consequences of urea-rationing for a longer period were tested and the dangers of thyroid-gland alterations were made apparent. Blood samples (120 cases) were taken in the experiment to determine the concentrations of NH3-N, urea and of thyroxine and triiodothyronine (480 pcs), referring to pre-test conditions. The same parameters were determined five times (every 2 months) during the experiment. The parameters received in the tests were, on average and in terms of extreme values as follows: [table: see text] Except for the histological outcome, the blood tests did not show the hypothyreosis of the whole organism.