Male infertility means the inability to sire a litter. It can be congenital or acquired. A stud dog who has never sired a litter despite several matings should be considered congenitally infertile. Congenital causes of infertility include chromosomal abnormalities (intersex), underdeveloped testicles (testicular hypoplasia), undescended testicles, and abnormalities of the penis and prepuce that prevent mating.
Acquired infertility occurs in a proven stud dog who subsequently becomes infertile. This follows testicular injuries and infections, and may occur as a consequence of prostatitis and infections of the male genital tract, such as brucellosis. Drug therapy, testicular degeneration, and immune-mediated orchitis are other causes of acquired infertility.
Hormone diseases of the pituitary and thyroid glands can cause both congenital and acquired infertility. Hypothyroidism is the most common hormonal cause of infertility. It affects both the dog’s sex drive and his sperm count.
Retrograde ejaculation is an acquired cause of infertility. It is caused by failure of the internal urethral sphincter to contract during ejaculation. As a consequence, the sperm are ejaculated into the dog’s bladder.
A significant cause of reduced fertility in males is excessive use. Dogs used at stud for three consecutive days should be rested for two days. Males with high fertility can be used every other day, but should be given periods of sex- ual rest to prevent overuse and loss of libido.
When a stud dog is used a great deal, a single mating may not be enough to cause pregnancy. Alternatively, a dog who has not been used for some time may have a low sperm count because of reduced production. During a second mating, two days after the first, the quality of the semen may be much improved.
Prolonged elevation of body temperature damages the sperm-producing cells. Some dogs are less fertile in the summer, especially if they live outdoors where the weather is very hot. A dog with a high fever may take several weeks or months to regain a normal sperm count. An age-related decline in sperm production occurs in older dogs.