Veterinarians, in conjunction with breeders, run a series of tests on the semen of stud dogs before breeding. Because the dog's stud fee often depends on the number of puppies he successfully sires, fertility tests are necessary for any successful breeding program. His age, his overall health and the number of times he ejaculates in a given period can influence the number of sperm the dog produces. A fertility evaluation tells the breeder how likely the stud is to impregnate the female and helps the breeder to determine when to retire the ageing stud.
Collecting the Semen
Veterinarians will commonly use a "teaser" bitch -- a female dog that is in heat -- and present her to the male dog to help him achieve an erection. After he is allowed to mount her, the vet will position the penis so that it enters an artificial vagina, a specialised plastic tube warmed to the body temperature of the dog. The male will be allowed to ejaculate into the artificial vagina and the collected semen will be kept warm and ready for laboratory analysis.
A veterinarian checking a semen sample for fertility will normally begin by using a small, hand-held instrument called a haemocytometer, which uses mathematical formulas to count the number of cells in a specific area. The vet will dilute a small portion of the semen with a chemical provided by the maker of that particular instrument; the chemical dilutions will vary from manufacturer to manufacturer. After a small portion of the diluted semen is placed on the loading platform of the haemocytometer, the vet will multiply the number of cells seen on a central square millimetre to calculate the total number of sperm cells per ejaculate. Normal count in dogs is 200 to 2,000 million sperm per ejaculation.
Veterinary sperm evaluation will typically include other laboratory tests to fully determine fertility. Since a high white blood cell count can indicate an infection that will lower sperm count, the number of leucocytes (white blood cells) in the ejaculate will be counted using the haemocytometer. Normal count is less than 2,000 per millilitre. The sperm will also be checked for motility (movement of the sperm through seminal fluid), morphology (any abnormalities in the size, shape and appearance of the sperm that would cause it to be ineffective) and the amount of seminal plasma alkaline phosphatase found in the sample. ALP is an enzyme found throughout the dog's bloodstream, but a low concentration found in the semen sample is an indication of incomplete ejaculation or an obstruction of the vas deferens, the tubes that carry seminal fluid from the testes to the penis. Other semen tests might include a check for bacteria and/viruses that can cause infertility.