The morphology of the thyroid glands of quails and fowls maintained on diets containing rapeseed.

Maintaining adult quails and fowls on diets containing rapeseed meal resulted in increased thyroid weight; this increase was greatest when ground, full-fat rapeseed was included in the ration. Thyroids of quails showed a relatively much greater enlargement than those of fowls. A biometric method indicated that the increase in hens and quails was associated with follicle enlargement. Light- and electron-microscopy showed that the thyroid epithelium of quails had frequently become tall columnar, due mainly to extensive dilation of the granular endoplasmic reticulum, and that electron-dense bodies and microvilli were increased in size and number. Vascularity increased and microhaemorrhages occurred. There was sometimes epithelial proliferation (hyperplastic goitre), particularly when the diet contained ground whole rapeseed. If smaller amounts of glucosinolates were offered for a longer period, electron-dense bodies were very enlarged. There were similar cytological reactions in fowls but these, particularly cisternal distension, were less prominent and the enlarged, colloid-filled follicles were usually lined by flat or cuboidal epithelium (colloid goitre). It was concluded that the morphological reaction of the gland is modified by amount of glucosinolate hydrolysis products, period of exposure and species of bird. The changes were discussed in relation to the toxicity of rapeseed to fowls.