Rapeseed Meals, Methimazole, Thiocyanate and Iodine Affect Growth and Thyroid. Investigations into Glucosinolate Tolerance in the Pig

Abstract

In two factorial experiments with a total of 81 growing pigs, the effects of antithyroid compounds and rapeseed meal (RSM) diets differing in glucosino-late content were tested without or with supplementary iodine. In Experiment 1, a 4×3 factorial arrangement was used to investigate the effects of antithyroid compound inclusion and supplementary iodine. Pigs received a grain–soya bean meal diet (control) or this diet with 250 mg kg-1 methimazole (MMI), 1000 mg kg-1 thiocyanate (SCN- as KSCN) or 80 g kg-1 high glucosinolate RSM (9·5 mmol glucosinolates kg-1), each diet supplemented without or with iodine; 0, 125 μg kg-1 (requirement) or 500 μg kg-1. In Experiment 2, a 5×3 factorial arrangement was used to study the effects of dietary glucosinolate content and iodine supplementation. Pigs received a grain–soya bean meal diet or four diets with 160 g kg-1 RSM differing in glucosinolate content (0·6, 2·4, 6 or 19 mmol kg-1 diet), each diet supplemented with iodine: 62·5 μg kg-1, 125 μg kg-1 (requirement) or 250 μg kg-1. Irrespective of the iodine dosage, MMI suppressed production of thyroxine and resulted in goitre, myxoedema and cretinism. SCN- induced clinical hypothyroidism when there was no supple-mental iodine. Despite high iodine supplementation, glucosinolate load (19 mmol kg-1 diet) decreased growth, feed intake, iodine store of the thyroid and serum concentration of thyroid hormone and resulted in goitre formation. In the case of diets with ⩽6 mmol glucosinolates kg-1, iodine prevented antithyroid effects. However, more iodine was required by these pigs than by control animals to a high T4 serum concentration. The lowest glucosinolate level tested (0·6 mmol kg-1 diet) yielded the same thyroid hormone status and thyroid weight as the control, however, the iodine content of thyroid gland was decreased. In conclusion, iodine administration prevents the effects of a low glucosinolate intake only, by overcoming the depressed thyroxine released of the thyroid, resulting in regression of goitre. © 1997 SCI.