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UBC Theses and Dissertations

Effects of chronic and early goitrogenic stimulation on thyroidal metabolism in the chicken and in the progeny Leung, Peter Chung Kwor


White Leghorn pullets were fed goitrogenic rapeseed meal or soybean meal during either or both the growing period and the laying period. Rapeseed meal was fed at a level of 17.5 percent of the starter-grower diet and 19.0 percent of the layer diet. Control rations contained 11.0 and 13.1 percent of soybean meal, respectively. The responses to the dietary treatments were studied when the birds were over 90 weeks of age. Parameters measured included: weights, histology and iodine contents of the thyroid glands, thyroidal I-131 uptake at different time intervals after administration of the radio-iodine, distribution of injected doses of radioiodine in iodinated substances in the thyroid glands, iodine contents of egg yolks, and the thyroidal characteristics of the progeny of these birds at hatching. Birds which were being fed rapeseed meal at the time the thyroid glands were examined showed effects which varied in magnitude according to the length of time over which rapeseed meal had been fed. Thyroid weights, follicle diameters, amounts of epithium and iodine contents of the thyroid glands of rapeseed meal-fed birds increased whereas coupling efficiency declined with time. The effects of overstimulation of the thyroid gland induced by the feeding of goitrogenic rapeseed meal during the growing period persisted for as long as 75 weeks after withdrawal of the source of goitrogen from the diet. Thyroid weights, thyroid iodine contents and radioiodine uptake were all increased in birds which had received goitrogen during the growing period. Follicle diameters were greater and heights of epithelial cells were lower in the thyroid glands of these birds than in those of the control. Eggs from rapeseed meal-fed birds were low in iodine. The thyroid glands of newly-hatched progeny from dams which had been fed goitrogenic rapeseed meal were observed to be hypertrophic. Since analysis of the eggs for goitrin was negative and analysis for iso-thiocyanates indicated similar concentrations in the eggs from birds fed rapeseed meal and from control birds fed soybean meal, the hypothesis was that the low concentration of iodine in the eggs of the goitrous birds was due to diversion of a large proportion of circulating iodine into the thyroid glands with the result that the amounts reaching the developing ova were reduced.

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