Thyroid Function in the Prenatal and Neonatal Bovine

A Considerable amount of research has been reported on some measures of thyroid development in the bovine fetus, as reviewed by Kossila (1967). Most of this research has been concerned with such aspects as thyroid growth and histological development, the appearance of iodinated components in the thyroid, and thyroidal uptake of radioactive iodine in the fetus and pregnant cow. Lewis and Ralston (1953) reported that calves less than 48 hr. old had higher plasma protein-bound iodine than older animals. Nathanielsz (1969) stated that plasma thyroxine (T4) of the calf is elevated in the first 3 hr. of extrauterine life. This is followed by a rapid fall in T4 level. Similar results were noted by Nathanielsz (1969) in newborn lambs. No information has been found on comparative levels of serum thyroxine (T4) together with the capacity of the specific carrier protein, thyroxine-binding globulin, to bind T4 in the pregnant cow and the fetal and neonatal calf.