developed symptoms of myxomatosis 7–10 days after infection and had high viral titers in testes. After 20–30 days, testes were 50% of normal size and affected animals had interstitial orchitis and epididymitis [42]. Protein and genomic studies of a porcine paramyxovirus had a close relationship to human mumps virus [43, 44], known to multiply in human testis, causing orchitis in postpubertal men [45]. Furthermore, when 9‐month‐old boars were experimentally infected with porcine paramyxovirus, histopathological epididymal alterations and testicular atrophy associated with degeneration of seminiferous tubules occurred [38]. In another study, colostrum‐deprived pigs were inoculated with porcine circovirus type 2 alone, porcine parvovirus alone, or with both viruses. All pigs that received both viruses became ill; at necropsy (21–26 days after infection), many had hepatomegaly and enlarged kidneys, with granulomatous lesions apparent in many tissues, including testis [46].
Obesity is associated with testicular degeneration and scrotal insulation has been used to produce testicular degeneration; however, scrotal insulation did not induce fibrotic lesions [4]. In one study, deficient, normal, and excessive dietary intakes did not affect prevalence of fibrotic lesions. However, with prolonged abnormal thermoregulation, especially when semen quantity and quality are very severely reduced, with loss of testis tone and size and with severe seminiferous tubular degeneration, scar tissue infiltration and testis fibrosis are plausible.
Trauma to the testes has also been proposed as a cause of testis fibrosis [10]. Trauma caused by a blow to the testes from kicking or butting could occur at any age, but may be more frequent during crowding in pens or handling in chute systems. Therefore appearance of fibrosis in conjunction with postweaning penning and feeding could be considered in the etiology of testis fibrosis. However, one of the authors observed a bull receive an acute blow to the testes with a metal pipe. Ultrasonography the following day and several times over the course of a month did not reveal any damage to the testes. Perhaps testis trauma, although common in penned bulls, does not cause fibrotic lesions.
Interestingly, fibrotic lesions in the testes were not associated with poor semen quality. Even bulls with very severe fibrosis produced semen with up to 94% morphologically normal sperm. Therefore presence of relatively large amounts of scar tissue within testis parenchyma did not prevent remaining unaffected parenchyma from producing normal sperm. Although large amounts of scar tissue would be expected to reduce sperm production, this has apparently not been reported.
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31 31