Bovine Reproduction. Группа авторов
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Ultrasonographic examinations in some groups of bulls in western Canada were done monthly from 3 to 15 months of age. In other groups in Canada and Argentina, ultrasonography was done after weaning at 5–8 months of age and repeated at 12–14 months of age in Canada and 18–20 months of age in Argentina. Testis assessment was done by orienting the transducer vertically on the scrotum and moving it 180° around the testis (both dorsal and ventral portions). Testes were scored for fibrosis from none to very severe, based on number and size of fibrotic lesions (Figures 13.1 and 13.2).
Figure 13.1 An ultrasonogram of testis scored as having mild fibrosis.
Figure 13.2 An ultrasonogram of testis scored as having very severe fibrosis.
Immunohistochemistry was performed on testis tissues of 10 bulls from the group affected by BRSV. Only one of these bulls had fibrotic lesions in testes. Testis tissue was submitted to a diagnostic laboratory for immunohistochemistry for BVDV and BRSV.
Fibrotic lesions scored as slight or mild were very common (31.3%) in testes of a group of bulls raised under intensive rearing conditions in western Canada. Only 2.5% had moderate scores and none had severe scores for fibrosis. In the more extensive management in Argentina, in a group not affected by respiratory disease associated with BRSV, fibrotic lesions were also mainly slight or mild, but incidence was higher (48.6%). In that group, 1.9% were scored moderate and 0.95% severe. In the Argentine group affected by BRSV, fibrotic lesion scores were higher and more frequent. Scores for slight to mild, moderate, and severe to very severe were 58.3, 17.1, and 5.7%, respectively.
Fibrotic lesions appeared as early as 5–6 months of age and number of cases continued to increase until at least 12–14 months. Lesion severity increased in some cases during this period, although it appears that lesion development occurred during a finite interval. There were indications that during fibrosis formation, spermatogenesis was adversely affected; however, presence of a large number of fibrotic lesions that may occupy as much as approximately half of testis parenchyma did not preclude production of a high percentage of morphologically normal sperm. In bulls with no, mild, moderate, or severe testis fibrosis, median percentages of normal sperm were 88, 87, 86, and 90% respectively. Lesion prevalence was not influenced by breed or testis size.
Histologically, lesions consisted of masses of fibrous tissue with fine fibrillation, or heavy bundles of wavy tissue seminiferous tubules. Usually there were fewer germinal cells in seminiferous tubules within masses of fibrous tissue. In some tubules, germinal cells and Sertoli cells were missing entirely and hyaline material was present in the lumen. Similar abnormalities were evident in seminiferous tubules adjacent to fibrous tissue masses; however, completely normal tubules were often beside or very close to fibrous tissue masses. Inflammatory cells were consistently absent. Therefore we inferred that neither the insult that caused fibrosis nor proximity of fibrous tissue to seminiferous tubules affected function of adjacent tubules.
With real‐time ultrasonography, many lesions appeared to extend from the rete testis toward the periphery of the testis and appeared to involve the entirety of one or more tubules at specific sites within the testis. This pattern was apparent in both gross sections (Figure 13.3) and in ultrasonograms (Figure 13.4). It appeared that entire tubules may be destroyed with replacement by fibrotic tissue. In other cases, there were isolated lesions in central or peripheral parts of testis parenchyma without extension to rete testis, implying tubular destruction occurred only at a specific site.
Figure 13.3 Cross‐section of a bull testis with fibrotic lesions that appeared to radiate from rete testis toward the periphery, suggesting individual tubules were destroyed and replaced by scar tissue.
Figure 13.4 Ultrasonogram of a testis with fibrotic lesions radiating from the rete testis toward the periphery.
The cause of the testicular fibrosis is uncertain. Potential causes are disrupted development of embryonic tubule‐to‐rete connections, an infectious disease process affecting tubule health and development, abnormal testes thermoregulation, and trauma.
Developmental changes of testes may be involved in development of fibrotic lesions. Tubularization of seminiferous cords within the testis tissue begins at ~4 months of age and is complete in nearly all bulls by 6 months [35]. Sperm release into tubules starts as early as 8 months and occurs in most bulls by 10 months. Therefore tubule impaction with sperm and tubule rupture with escape of sperm into the peritubular space of the testis tissue would not be expected to occur much before 8 months. Because sperm are antigenically foreign, a tissue reaction against escaped sperm could cause fibrosis. Impaction of seminiferous tubules might be due to congenital failure to develop a tubular connection to the rete tubules. Tubule rupture and a tissue reaction against sperm should not occur until testes produce sperm; as production increases, testes lesions would be expected to increase in number and severity.
Bacterial and viral infections are common in early post‐weaning period when maternal immunity has waned and animals of multiple origins intermingle [36]. Thus an infectious process, as a cause of fibrotic lesions, would fit the time period when testis lesions appear in young bulls. Although bacterial or viral infections would be expected to cause testicular swelling and pain, perhaps inflammation is mild and not apparent. Infectious agents could cause inflammation of arterioles and capillaries in the testes, leading to local tissue necrosis and formation of foci of fibrosis [10]. Viral infections may also target specific cells within seminiferous tubules, e.g. Sertoli cells or individual germinal cells, resulting in tubule damage and fibrous tissue infiltration [37, 38].
Two common viral diseases of cattle, bovine herpesvirus (BHV)‐1 and BVDV, have been investigated for their role in male reproductive infections. Both viruses have been isolated from semen [39, 40] and BHV‐1 has been associated with degenerative changes in the seminiferous epithelium, perhaps due to illness and fever [41]; however, there are no reports that associate BHV‐1 or BVDV with lesions in bovine testes.
The association of a greater prevalence of testis fibrosis with occurrence of a severe outbreak of BRSV respiratory disease in the Group 1 bulls in Argentina, combined with a lesser prevalence of testis lesions in Group 2 (vaccinated against BRSV), suggests that BRSV may be involved in etiology of testis fibrosis. However, immunohistochemistry of testis tissues from 10 bulls that were culled and slaughtered from Group 1 failed to detect BRSV antigen. Failure to find evidence of BRSV antigen may indicate that this virus does not multiply in testis tissue or it might be due to the lack of fibrotic lesions in 9 of 10 of the testes from which samples were submitted and because samples were obtained ~12 months after BRSV incident.
Viral agents multiply within the testes of several