Mitogenic action of estrogen on thyroid gland of male domestic duckling.

Intramuscular administration of estradiol dipropionate (OVOCYCLIN: CIBA, India) with a daily dosage of 1 mg per bird for 10 days, to male domestic ducklings, induced mitosis in the thyroid gland. Concomitantly, it decreased follicular epithelial height and increased colloidal material in the follicles. It is suggested that estradiol appears to have a dual action on the thyroid gland of the male duckling, since it accelerates mitosis but inhibits thyro-follicular activity of these birds.