According to "Dog Owner's Home Veterinary Handbook" (Debra M. Eldredge, DVM, et al, 2007), a female dog that mates only once with a chosen stud often does not get pregnant because the sperm count of the stud has been affected. Because dog breeders often use artificial insemination, high sperm count has become more of a concern.
Frozen dog sperm can last a considerable length of time. According to MSNBC, one German Shepherd's sperm could still sire pups 34 years after it was banked. But not every dog owner can afford to bank frozen sperm for 34 years. Many people use fresh sperm for artificial insemination and that sample needs to have as many healthy sperm cells as possible to fertilize the female.
A normal sperm count in a dog has at least 250 million sperm in a semen sample. There can be more in a sample. Over 70% need to be active, healthy sperm in order for the stud dog to be considered fertile. Any number less than 100 million sperm in a sample usually means that the dog has health issues that are affecting his fertility.
Size of Female
If a female dog is going to be bred by artificial insemination, then she needs a dose that relates to her body weight. A dog less than 10 pounds (or 5 kilograms) needs a 1.5 - 3 milliliter insertion. A dog weighing up to 50 pounds (or 25 kilograms) needs 3 milliliters of semen. A dog weighing over 50 pounds needs 5 - 8 milliliters of semen.
A dog can have very low sperm count due to genetics, a deformity of the genitalia, side effects from medications or a health problem. Common health problems that lower sperm count include fever, pituitary gland problems, testicular cancer, hypothyroidism or other problems with the thyroid glands. Dogs also will normally have the highest sperm counts before they are 7 years old. As the dog ages, sperm count will decline. This is a normal part of aging.
If a stud dog is bred too often, this will definitely lower his sperm count. "Dog Owner's Home Veterinary Handbook" recommends that stud dogs only be bred for three days in a row and then given a rest for two days before breeding again. Dogs that have not been bred in months may have a low sperm count in the first breeding but a higher sperm count in the second breeding.
Stud dogs are best kept indoors at room temperature in order to have the best chance at producing a normal sperm count. They also need to be healthy, since any illness can affect a dog's entire reproductive system. Just as fevers can reduce a dog's sperm count, so can being kept in very hot or humid conditions.