Spontaneous testicular lesions in purpose-bred beagle dogs

Spontaneous testicular lesions were assessed in 50 control purpose-bred mal e beagle dogs. They were selected from 13 toxicology studies conducted over the period 1988-1999. Age of the dogs at study termination varied from 8-2 0 months with an average age of 13 months. Regardless of age, the most sign ificant finding was bilateral segmental hypospermatogenesis in 15/50 (30%) of the dogs. Cross sections of tubules with hypospermatogenesis were distri buted randomly throughout the testes and were characterized by reduced prop ortions of germ cells, tubular shrinkage, and Sertoli cell prominence. Thes e changes were occasionally associated with giant cells, with cellular debr is, and in 6/15 (40%) with atrophic tubules devoid of germ cells, indicatin g a degenerative process. Focal subcapsular tubular atrophy or hypoplasia ( tubules Lined by Sertoli cells only) was also found in 9/35 (26%) of dogs w ithout hypospermatogenesis. Inhibited spermiation with retention of mature sperm in tubules was seen in 6/50 dogs, 3 of which also showed hypospermato genesis. Other findings of high incidence but low prevalence included tubul es with multinucleated giant cells, swollen spermatocytes, or apoptotic ger m cells. These latter changes are probably a constituent of normal spermato genesis. In conclusion, about 30% of control beagle dogs show segmental hyp ospermatogenesis, which may be associated with degenerative changes, and an additional 18% of the dogs exhibit focal tubular atrophy/hypoplasia in oth erwise normal testes. These changes have to be distinguished from compound- related toxic effects.