Age-related changes of seminiferous tubule morphology, interstitial fibrosis and spermatogenesis in dogs

There are age-related changes in testicular anatomy and physiology whereby there are modifications of sperm production and reproductive hormone functions. Effects of age on testicular microanatomy are well documented in humans, while there is limited understanding of these changes in dogs. The aim of this study was to evaluate age-related changes of seminiferous tubule morphology, interstitial fibrosis and spermatogenesis in dogs. Dogs (n = 32) were divided into four age groups: peripubertal (n = eight), relatively younger (n = seven), reproductively mature (n = seven) and relatively older (n = ten). Picrosirius Red stained sections were used for morphometrical analysis of testicular tissues, while the characteristics of seminiferous epithelium were assessed using a modified Johnsen scoring system for haematoxylin and eosin stained sections. Seminiferous epithelium and seminiferous tubule area increased from peripuberty to reproductive maturity, indicating there were changes during sexual maturation and subsequently there were decreases with further aging. There was a similar age-related trend for changes in seminiferous epithelium height with values being greatest in reproductively mature dogs; while there were no age-related differences in tubular diameter. Collagen content in the testicular interstitium gradually decreased from peripuberty to the age when dogs were reproductively mature and there were subsequent increases in relatively older dogs, thus, there was an association between the extent of testicular fibrosis and senescence. There was a decrease in spermatogenetic functions from relatively younger to older ages. Further investigations are warranted to establish mechanisms responsible for age-related changes of testicular morphology and related clinical implications.