Effects of alterations in maternal thyroid metabolism on embryonic thyroid development in the chick.

The cause of embryonic thyroidal enlargement in the progeny of chickens fed goitrogenic rapeseed meal (RSM) has been investigated. It has been found that eggs from birds fed RSM are low in iodine. The low concentration of iodine in the eggs of the goitrous birds is apparently due to diversion of a large proportion of the circulating iodine into the thyroid glands with the result that the amounts reaching the developing ova are reduced.