Age-related testicular degeneration is a common problem in older stallions. This type of testicular degeneration is different than the degeneration that can be seen after, for example, an injury to the testes in a younger stallion. Following testicular trauma, many stallions are able to fully recover. However, age-related testicular degeneration results in progressive deterioration of the testes and an associated progressive decline in testicular function. Over time, affected stallions become progressively more subfertile and eventually may become sterile in association with decreases in semen quality, sperm numbers and testicular size. There is no proven treatment for age related testicular degeneration, although many therapies have been tried. In this article, Dr. Regina Turner of the New Bolton Center at the University of Pennsylvania, discusses the causes of age-related testicular degeneration, current research and how one can manage the breeding career of an aged stallion until a treatment or cure is found.