Pathology and familial incidence of orchitis and its relation to thyroiditis in a closed beagle colony

Lymphocytic orchitis occurs spontaneously in a closed colony of beagle dogs with an incidence of 32% among 69 untreated males over 1 year of age. This disease is genetically influenced as determined by an analysis of the ancestral composition of each animal. Orchitis is related in its occurrence to lymphocytic thyroiditis which has been previously described in this colony. The incidence of both diseases increases with increasing degrees of relatedness to three sibling progenitors of a partially inbred line which comprises a significant portion of the colony. Among the dogs that derived all of their genes from the three progenitors, 85% had lymphocytic thyroiditis and 65% had lymphocytic orchitis. The pathologic changes in the testes result in a significant reduction in testis size and weight as well as sterility or reduced fertility.