THE EFFECTS OF FOETAL THYROIDECTOMY ON THE DEVELOPMENT OF THE OVINE FOETUS

Abstract

SUMMARY Thyroid glands were surgically ablated from foetal sheep between 81 and 96 days of gestation in order to study the role of the thyroid gland in foetal development. Gestation of ewes bearing thyroidectomized foetuses was prolonged by about 5 days, and athyroid lambs failed to survive more than 24 h. Athyroid foetuses delivered by Caesarian section 1 week before term were characterized by low body weight, low thymus gland weight, and shortened limbs. Foetal thyroidectomy markedly retarded both the maturation and growth of wool follicles and osseous tissue. Plasma concentrations of growth hormone, calcium and phosphorus were normal in the athyroid foetuses, but cholesterol levels were increased. The absence of thyroxine in the foetal circulation agrees with previous findings that the ovine placenta is impermeable to maternal thyroxine.