THE EFFECTS OF PARTIAL THYROIDECTOMY ON THE DEVELOPMENT OF THE EQUINEFETUS

A syndrome of congenital hypothyroidism and dymaturity has been an imp ortant cause of reproductive loss and foal mortality in western Canada , The cause and pathogenesis of this syndrome is under investigation, One issue to be addressed is whether all the anomalies present in affe cted foals are produced concurrently by the same agent, or if affected foals are primarily hypothyroid in utero which induces the associated lesions. This study was designed to document the effects of fetal thy roidectomy, at about 215 days of gestation, on the growth and developm ent of the equine fetus and to compare the anomalies present to those reported in the spontaneously occurring syndrome of foals in western C anada. Two sham-operated controls and 4 partially thyroidectomised foa ls were carried to term following surgery, Sham-operated control foals were normally developed, Partially thyroidectomised foals were hypoth yroid; had hyperplastic thyroid gland remnants; abnormal behaviour and locomotor skills; and numerous, marked deficiencies in their skeletal development, The anomalies present in partially thyroidectomised foal s were comparable to those reported in congenitally hypothyroid neonat es of other species, including human infants, and were similar to thos e described in congenitally hypothyroid and dysmature foals reported i n western Canada.