Prepubertal exposure to the live attenuated avian infectious bronchitis virus induces epididymal stones in the rooster after puberty

Roosters immunized prepubertally with the avian infectious bronchitis virus (AIBV) have a high incidence of epididymal calcium stones, reduced daily sperm production and lower serum testosterone as adults. The aim of the present study was to determine when and how stones are formed following vaccination with AIBV. Specific pathogen free roosters were either immunized with the live attenuated AIBV (vaccinated group, n = 38) or with the vehicle (nonvaccinated group, n = 33) at 2, 6 and 10wk of age. Testes and epididymides were studied histologically at 12, 16, 20 and 26 wk of age. Abnormalities were not observed in testes of either vaccinated or nonvaccinated group at any age observed. The epididymal region of the vaccinated group was normal until 16 wk. However, aggregations of sperm, cell debris and macrophages and stones were present in the proximal efferent ductules in the vaccinated group at 20 wk and 26 wk of age. These efferent ductules showed expanded lumen, reduced mucosal folds and low columnar epithelium. Next to these affected ductules were normal efferent ductules. On the other hand, epididymal stones also occurred in the nonvaccinated group (2/18, 25%) at 26 wk but the frequency was lower than that in the vaccinated group (8/14, 57%). These results indicate that epididymal stone formation begins with aggregations of sperm, cell debris and macrophages immediately after puberty, which is followed by calcium deposition. It is suggested that the prepubertal vaccination with AIBV accelerates epididymal stone formation.