Some aspects of thyroid metabolism in the chicken

• Main Author: Poon, Raymond Wai-Man
• Language: English
• Published: 2010
• Subjects: Deficiency diseases in poultry; Poultry > Diseases
• Online Access: http://hdl.handle.net/2429/20390

The study of thyroid metabolism usually involves the employment of antithyroid compounds and exogenous thyroid hormones in order to elucidate the thyroid function through the understanding of the effects of these compounds. In this study, the effects of die thiouracil and rapeseed meal goitrogens were examined in chicks. The goitrogenic effects of the thiouracil were manifested rapidly by increased thyroid weight, thyroid epithelium and uptake of radioiodine. The goitrogenic effects of rapeseed meal were similar to the effect of thiouracil except that at the level of meal fed, the effects were less pronounced and evident only after prolonged feeding. When an iodine deficient diet was fed to growing chicks, the goitrogenic effect was less than when thiouracil or rapeseed meal was fed. Histological studies of the thyroid glands of adult birds fed an iodine deficient diet showed slight hyperplasia without thyroidal enlargement and with persistence of colloid,whereas growing chicks fed an iodine deficient diet displayed severe hyperplasia and loss of colloid. By contrast, the effects of thiouracil were independent of the age of chicks. A combination of thiouracil and rapeseed meal produced goitrogenic effects greater than those occurring when thiouracil or rapeseed meal was fed singly. Thiouracil fed in an iodine deficient diet, on the other hand, showed no goitrogenicity for chicks. High doses (4.0 μg) of thyroxine administered daily to thiouraci1-treated chicks alleviated the antithyroid effects of thiouracil as indicated by the decrease in thyroid weight, thyroid epithelium and radioiodine uptake. Low doses (1.0 ug or less) of thyroxine administration, however, produced the opposite effects. Nevertheless, high doses of thyroxine did not relieve the growth depressing effects of thiouracil completely. Autoradiographic studies on thyroids of thiouraci1-treated or rapeseed meal-fed chicks showed a uniform distribution of radioiodine in the colloid within five hours of administration of tracer. Differences in activity were observed among the individual follicles in each gland. The smaller follicles concentrated more iodine than the larger ones. Furthermore, very little iodine was observed in the epithelial cells. These findings, together with previous reports that inorganic iodine was present in the thyroid after its administration, suggested that iodination did not occur in the apical membrane of the follicular cells bordering the colloid. Different rapeseed cultivars contain different amounts of glucosinolates which are responsible for the goitrogenic effect of the rapeseed meal. Goitrogenicity of three different kinds of rapeseed meals was compared in growing chicks and the results indicated that Candle meal had the least goitrogenic activity than the Tower and Span meal. === Land and Food Systems, Faculty of === Graduate