Histopathological and histomorphometric testicular characteristics associated to reproductive condition in Bos indicus (Nellore) bulls

The aim of this study was to evaluate morphological, morphometric and functional aspects of spermatogenesis based on reproductive conditions of Nellore bulls. The study used 25 bulls Bos indicus (Nellore), which were classified as satisfactory (n=10) and unsatisfactory (n=15) for reproduction. After orchiectomy, fragments of the right testis of each animal were processed routinely and stained with hematoxylin and eosin (HE) and periodic acid-Schiff (PAS). The slides were analyzed in bright field microscopy at different magnifications. The tubular segments were classified into four levels (normal, mild and moderate degeneration, severe degeneration, and tubular hypoplasia) based on the organization and architecture of the tubular tissue. The average height of the seminiferous epithelium, the average thickness of propria tunic and the average tubular diameter were obtained and the proportion of seminiferous tubules, interstitial tissue, lymphatic vessel and blood vessel of each bull testicle were recorded. Furthermore, the frequency of the three classifications of the spermatogenic cycle A, B and C (A = group of stages I, II, and III which comprise the initial phases of the cycle and mitotic proliferation, B = group of stages IV and V, which comprise intermediate phases and intensive mitosis, C = group stages VI, VII and VIII which comprise the final phases and post-meiosis) was compared. The results showed that the degenerative changes in germ cells are associated with histomorphometric variations, including those in the density of the structures that comprise the testicular parenchyma, and are more representative in bulls with poor semen quality. In addition, the unsatisfactory bulls for reproduction showed reduced meiotic potential compared to that of satisfactory reproductive bulls.