The Thyroid Hormone and Immunoglobulin Concentrations in Blood Serum and Thyroid Gland Morphology in Young Hens Fed with Different Diets, Sources, and Levels of Iodine Supply

SIMPLE SUMMARY: Bioactive micronutrients, such as iodine, regulate many key metabolic pathways in the body. Iodine is responsible, above all, for proper functioning of the thyroid gland and the hormones it secretes, which, in turn, determine the correct course of many processes. There is a close relationship between the level and source of iodine in the diets of animals and the activity of the thyroid gland. In addition, attention should also be paid to the presence in the diet of compounds that can decrease iodine utilization, such as the goitrogenic substances present in some feed materials. The examined effects of various sources and levels of iodine, as well as the presence of rapeseed meal in laying hen diets, indicated that the applied iodine sources and levels had no influence on thyroid hormone and immunoglobulin concentrations. However, iodine presence in the rapeseed meal diet and higher iodine concentrations can increase free triiodothyronine concentrations in blood serum. The level and source of iodine had an effect on the follicular diameter and height of the follicular epithelium cells. ABSTRACT: The aim of this study was to examine the influence of the level (1, 3, and 5 mg I/kg) and source of iodine (KI, Ca(IO(3))(2), and KIO(3)) on thyroid hormone and immunoglobulin concentrations in the blood serum of laying hens alongside a histological picture of the thyroid. In the first, birds were fed grain–soybean meal mixtures, and in the second, two kinds of diets based on corn–soybean or corn–soybean–rapeseed meal were applied. In the experiments, we determined the levels of the blood serum thyroid hormones fT(3) and fT(4), as well as the morphological structure of the thyroid gland. In the second experiment, the concentration of immunoglobulins in blood serum was assayed. In both experiments, no influence of iodine source on thyroid hormone concentration was observed. However, increasing the iodine level in the full mixture and adding rapeseed meal in both experiments caused an increase in fT(3) concentration. Increasing I-addition in both experiments led to a decrease in thyroid gland follicle diameter. Rapeseed meal inclusion (at a level of 10%) to the complete hen mixture led to an increase in thyroid gland follicle diameter. Applying KIO(3) as an iodine source in both experiments caused a decrease in the thyroid gland height of follicle epithelial cells. Immunoglobulin concentrations in the serum were not affected by experimental factors. The results suggest that the methodologies of studies on the bioavailability of minerals and the corresponding analytical methods require unification. The lack of such standardization makes it impossible to engage in a satisfactory discussion of the results and exchange experiences.