Goitrogenic effects of extracted rapeseed meal and nitrates in sheep and their progeny

Veterinarni Medicina 45, 2000, 129-140

Three groups of the breed Sumava sheep were fed meadow hay completed with extracted rapeseed meal, containing 4.2 mmol of glucosinolates, and 4 g of sodium nitrate per animal per day for 382 days. Moreover, two of the groups received parenterally 0.25 mg iodine and 0.15 mg sodium selenite per animal and per day at weekly intervals. The fourth group, also supplemented with iodine and selenium, was fed a diet without the addition of nitrate in which extracted rapeseed meal was replaced with oats meal. Biochemical analyses included determination of iodine concentrations in colostrum and milk of ewes and iodine, thyroxine and triiodothyronine concentrations in blood plasma of lambs from birth up to the age of 60 days. Thyroids of five necropsied lambs were weighed and examined by light and electron microscopy. Hypothyreosis with sporadic occurrence of congenital goitre and low concentrations of iodine and thyroxine in blood plasma were observed in the progeny of the ewes receiving in their diet extracted rapeseed meal and nitrate without iodine and selenium supplementation. The histological structure of the enlarged thyroid indicated 3rd stage of goitre. Electron microscopy revealed multilayer arrangement of follicles, cystic extension of cisterns of the endoplasmatic reticulum, numerous activated mitochondria, and pyknotic nuclei displaced towards the cytoplasmatic membranes of thyreocytes. Biochemical analyses demonstrated low concentrations of iodine in colostrum and milk (57 +/- 36 and 27 +/- 15 mu g/l, respectively) and of iodine and thyroxine in blood plasma of lambs (69 +/- 24 mu g and 101 +/- 27 nmol/l, respectively). On the other hand iodine concentrations in colostrum and milk were significantly (P < 0.01) higher in the groups receiving the same doses of goitrogens, but supplemented with iodine alone (colostrum 334 +/- 330 mu g/l

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