The normal testicle is smooth, oval, and has a regular outline. Both testicles should be of similar size and feel rather firm. The size of the testicle is related to its sperm producing capacity. Accordingly, small testicles in a sexually mature dog produce a smaller number of sperm. The diagnosis of testicular disease can be confirmed by biopsy.
Testicular hypoplasia is a developmental disorder in which one or both testicles fail to reach normal size at sexual maturity. The small size and flabby consistency of these testicles is caused by poor development of sperm-producing tissue. An ejaculate will show either no sperm or a low number of sperm with numerous abnormal forms. There is no effective treatment.
Testicular degeneration is an acquired disease that can result in either permanent or temporary sterility. Unlike testicular hypoplasia, the testicles were normal before they became small. A common cause of reversible testicular degeneration is high fever. Effective sperm production requires that the scrotal temperature be at least two to three degrees below the core body temperature. Fever raises both body and scrotal temperatures. Diseases associated with fever that can cause temporary testicular degeneration include canine distemper, parvovirus, and leptospirosis. Hypothyroidism is also a major cause of infertility in mature male dogs. If any of these conditions persist, permanent infertility can occur.
Immune-mediated orchitis occurs following testicular biopsy and trauma in which sperm escape and enter the bloodstream. The escaped sperm cause the body to produce antisperm antibodies. The antibodies destroy the sperm in the dog’s own testicles.
In all the conditions just described, the testicles become small and flabby like those of a dog with testicular hypoplasia.
There are also diseases that destroy the testicles: These are testicular trauma and acute bilateral orchitis. In testicles damaged in this way, the sperm-producing tissue is replaced by fibrous connective tissue. The testicles become small and hard. Sterility is irreversible in these cases.
Treatment: Testicular degeneration is treated by correcting the underlying disease and allowing time for spontaneous recovery. Sexual rest is essential. Semen examinations are used to monitor the return of spermatogenesis. It takes 50 to 60 days for regenerating sperm to reach the ejaculate, so any improvement in sperm quality will not be seen for at least two months.