Hyperplasia of the thyroid gland and concurrent musculoskeletal deformities in western Canadian foals: reexamination of a previously described syndrome.

A syndrome of neonatal foals characterized by hyperplasia of the thyroid gland and concurrent musculoskeletal deformities (TH-MSD) has been described in western Canada and may be increasing in incidence. In an attempt to improve recognition and understanding of this syndrome, 2946 records of equine abortuses, stillborns, and dead neonatal foals were examined to determine the laboratory involved, the year and month of submission, the breed and sex of the fetus or foal, the type of perinatal loss, the length of gestation, and whether or not the submission had evidence of a lesion of the thyroid gland, the musculoskeletal system, or other abnormal clinical or postmortem findings. One hundred and fifty-four (5.2%) records indicated the presence of an abnormal thyroid gland. Of these, 79 (2.7%) had additional lesions consistent with the TH-MSD syndrome described in the 1980s, while 75 (2.5%) were without these additional lesions. Comparisons among these two groups and a third group of fetuses and foals without lesions of the thyroids glands are described. The results confirm that the TH-MSD syndrome is a specific and unique disease with no breed or sex predilection. It is argued that there may be an "exposure-related" cause, and based on a review of similar disease syndromes of the horse, it is suggested that an examination of the feed is indicated in outbreaks of the TH-MSD syndrome.