Abstract
Both oxazolidinethione (OZT) and isothiocyanate (ITC) are known as main cleavage products of glucosinolates in rapeseed meal. Experiment 1 was conducted with day-old White Leghorn male chicks to study antithyroid effects of OZT and ITC. The basal diet used in this study consisted mainly of corn and soybean meal and it contained 0.67μg iodine/g diet. Thyroid glands of chicks administered OZT (premixed in the basal diet at 0.05% level) for 14 days were enlarged about three times that of the control chicks fed the basal diet. On the other hand, thyroid glands of chicks administered ITC (resolved in ethyl alcohol and premixed in the basal diet immediately before feeding at 0.05% level) for 14 days were slightly enlarged. Thyroidal 131I uptake in the chick was stimulated by OZT and it was suppressed by ITC. The stimulating effect of OZT contradicted the suppressing effect of ITC when both were administered to the chick simultaneously. The results of the present study indicate that antithyroid effects of ITC are considerably weaker than that of OZT.
In experiment 2, effects of autoclaving on elimination of OZT and ITC in the rapeseed meal of B. napus and B. campestris were examined. After autoclaving at different conditions, OZT and ITC in the rapeseed meal were determined. The higher the temperature and the longer the time of autoclaving, the smaller amount of OZT and ITC remained in the rapeseed meal. But, the rate of diminution of OZT did not coincide with that of ITC in the autoclaved rapeseed meal. Contents of OZT and ITC in the rapeseed meal of B. campestris were lower than those in the rapeseed meal of B. napus and the rates of diminution of these compounds in the autoclaved rapeseed meal were different between the spacies of rapeseed.
In experiment 3, thyroid weight and thyroidal 131I uptake in the chicks, fed rations containing autoclaved rapeseed meal at 24% level for 14 days, were investigated. Thyroid weight index (thyroid weight in experimental group/thyroid weight in the control group) in the chicks fed the autoclaved rapeseed meal containing diet did not increase so much as expected from the content of OZT in the ration. And, thyroidal 131I uptake in the chicks fed the autoclaved rapeseed meal diet was almost the same as that in the chicks fed the control diet. These results may indicate that the amount of OZT which might be formed in the intestinal tract of the chick is very small when myrosinase activity in rapeseed meal has been inactivated beforehand.
