Pathology and familial incidence of thyroiditis in a closed beagle colony

Abstract

Lymphocytic thyroiditis, resembling Hashimoto's disease of man, occurs spontaneously in a closed breeding colony of beagle dogs with an incidence approaching 20% among untreated animals over 1 year of age. This disease is genetically influenced as determined by an analysis of the ancestral composition of each animal. The incidence increases with increasing degrees of relatedness to three sibling progenitors of a partially inbred line which comprises a major portion of the colony. The pathologic changes in the thyroids cause neither clinical signs nor enlargement of the gland, and the severity of the lesions is independent of age. The lesions do not appear to be progressive in severity or result in atrophy or fibrosis of the gland. The histologic features and total incidence of thyroiditis in adult dogs given lethal or near-lethal doses of ionizing radiation is distinctly different from those of nonirradiated dogs, but the incidence is genetically influenced in the same manner as in nonirradiated adults. Lymphocytic lesions also occur in the thyroids of 55% of stillborn puppies but are dissimilar to those in all adult dogs. The incidence of these lesions, however, is not genetically influenced as are those in adult dogs. Therefore, the diseases in neonatal and adult dogs are different.