Hypoplasia is the term that is used to describe underdevelopment or incomplete of the testes. It is an inability to grow and mature properly. 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. Smaller than normal testes are generally easy to spot. 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.
Degeneration refers to the loss of potency after the stage of puberty has arrived. It is an acquired disease that can result in either permanent or temporarily 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 2 – 3 degrees below the core body temperature. Fever raises both body and scrotal temperatures.
Both conditions, hypoplasia and degeneration of testes, are congenital or can be due to some other cause that takes place after the birth.
Dogs of any age or breed are predisposed to these conditions, but hypoplasia is most commonly seen in young dogs, and degeneration is more common in older dogs.
Besides abnormally small testicles, infertility is the most common symptom of these conditions. Either low sperm count or absolute absence of sperm is found in the semen analysis of such dogs.