Feeding of rapeseed presscake meal to pigs: effects on thyroid morphology and function and on thyroid hormone blood levels, on liver and on growth performance.

Effects of feeding soybean meal (SBM) or a mixture of SBM and 5%, 10% and 15% of either 0- and 00-rapeseed presscake meal (RPM) on thyroid, liver and growth performance were studied in castrated boars. Goitrin (G) intake was closely correlated with total glucosinolate intake and blood thiocyanate concentration. In pigs fed 10% and 15% 0-RPM refused feed was enhanced and daily gain decreased. Liver weight and DNA/total liver increased with increasing G intake. Thyroid weights increased up to a G intake of 4.6 mmol/d and then decreased with higher G intake. DNA content/g dry matter (DM) increased continuously and total thyroidal DNA content up to a G intake of 4.6 mmol/l, indicating hyperplasia. Epithelial thickness increased up to a G intake of 13.3 mmol/d, whereas follicular area only up to an intake of 4.6 mmol G/d and then decreased, mirrored by a decrease of DM content. Thyroidal thyroxine (T4) and triiodothyronine (T3) content decreased with increasing G intake. Blood serum levels of T4 decreased with increasing G intake, whereas T3 levels only tended to decrease. Therefore, measured parameters differently reacted to different G intake. In groups fed high amounts of G, hyperplasia was not sufficient to maintain physiological circulating T4 levels, but enhanced thyroidal secretion T3 and/or extrathyreoidal T4 to T3 conversion obviously allowed maintenance of near normal circulating T3 concentrations and barely reduced growth rate despite marked hypothyroidism.