A complete breeding soundness examination in dogs consists of a history, physical examination, semen evaluation, and testing for Brucella canis . If infertility is suggested from the history, it should be established that adequate breeding management was practiced and that bitches had normal fertility when bred to other dogs. The time sequence of litters sired and bitches that did not conceive should be recorded, as should any recent illness during or before the time that the bitches were bred. These should be assessed to determine if the infertility may be transient (eg, fever can adversely affect semen production for >60 days after the initial insult).
A general physical examination should be performed. Dogs with abnormalities such as severe joint disease or spinal problems may not be able to mount. Endocrinopathies such as hyperadrenocorticism or hypothyroidism may reduce fertility; these may be associated with abnormalities in weight or hair coat. The penis and prepuce should be examined; problems such as persistent frenulum, growths, or swelling due to balanoposthitis may prevent normal intromission. Abrasions or lacerations on the penis may bleed during coitus, and blood may be seen in the semen. The prostate should be digitally palpated per rectum; prostatitis may be painful, causing the dog to be unable to finish a mating or appear to have lowered libido. In addition, WBC, RBC, and bacteria from an inflamed prostate may decrease sperm viability, and infection of the prostate can potentially ascend to cause orchitis. The scrotum, testicles, and epididymides should be palpated. Small, soft testicles are usually associated with poor semen quality; greatly enlarged testicles suggest orchitis or epididymitis. Lumps suggesting neoplasia may be palpable. Scrotal abnormalities such as dermatitis may adversely affect semen quality by decreasing scrotal thermoregulation. Length, width, and diameter of testicles should be measured with blunt calipers; these measurements are often of value for future comparison in cases of suspected testicular degeneration. Ultrasonographic examination of the scrotal contents is valuable to evaluate presence of testicular or epididymal masses.
Semen collection is performed with the dog on good footing (eg, a rug) rather than on a slippery surface or table. Care should be taken to intimidate the dog as little as possible; lifting the dog to an examination table, giving injections, etc, should be performed after the semen is collected. Semen may be collected in the absence of a bitch (although sperm numbers may be lower), but the presence of a bitch is preferable . The pheromone methyl paraben may be helpful for collection in the absence of a bitch; some veterinarians freeze swabs of estrous bitch urine for this purpose but the reaction of male dogs is variable. A collecting cone such as the liner of a bull artificial vagina (AV), lubricated with sterile
non-spermicidal lubricant or petroleum jelly and attached to a test tube, is used. The penile sheath is gently pulled back and the cone is slipped over the penis. As soon as the bulbus glandis is
exteriorised from the sheath and is within the cone, the penis is grasped through the cone, immediately caudal to the bulbus. Constant pressure is maintained caudal to the bulbus, and erection and eventually ejaculation should be achieved. Scratching the dog’s chest and speaking encouragingly may be helpful. If a bitch in estrus is available, the penis should be diverted into the cone as the dog mounts. Contact of the penis with the lubricated cone typically stimulates the dog to thrust into the cone, and the penis is compressed through the cone caudal to the bulbus as described above.
If no cones are available, or it is suspected that the dog’s semen is sensitive to the rubber in the cone, a gloved hand (using a non-latex glove) can be used to compress the unsheathed penis caudal to the bulbus glandis, and the semen collected into a urine specimen cup or waxed drinking cup. The rim of the specimen cup should be taped to prevent cutting the penis if it should contact the cup. Some breeders simply use a plastic bag held over the penis to collect semen.
The first (clear) fraction and the second (sperm-rich, cloudy) fraction should be collected. After these fractions are ejaculated, close inspection of the collection tube should demonstrate that clear fluid is starting to layer on the cloudy second fraction; at this point, the collection may be stopped. The dog may continue to ejaculate prostatic fluid for up to 10 min before the erection subsides. The sheath should be examined after the penis is retracted to ensure that the penis is situated normally within the sheath and that no hair is caught within the sheath. Residual protrusion may occur if the sheath rolls inward as the penis retracts.
Semen evaluation consists of determination of appearance, volume, concentration, motility, and percent morphologically normal sperm. Yellow, brown, or red samples may indicate the presence of blood or urine in the ejaculate. The volume is variable, depending on how much prostatic fluid was collected and the size of the dog; it ranges from <2 to >20 mL but is typically ~5 mL. Sperm motility should be evaluated immediately using warmed equipment; sperm should be >70% progressively motile spermatozoa. Sperm morphology is determined as for the bull ( Cattle). At least 80% of the sperm should be morphologically normal. The concentration is determined using a hemocytometer. To do this, the sperm is diluted at 1:100, and the number of sperm in the large central square (made up of 25 smaller squares) on the hemocytometer is counted. The number of sperm counted × 106 is the concentration of spermatozoa/mL. The total number of sperm in the ejaculate is calculated as volume × concentration. This should be =200 × 106, and closer to 400 × 106 in larger dogs.
Every dog investigated for infertility should be screened for Brucella canis. (See also Brucellosis in Dogs)
Sperm quality may be normal or abnormal, or no sperm may be seen in the ejaculate. Infertility is rare in dogs with a normal sperm evaluation and, if seen, the history should be reviewed for mismanagement or bitch infertility. The presence of WBC or RBC in the ejaculate suggests inflammation of the tract, most commonly prostatitis; culture of prostatic fluid and appropriate treatment may help fertility. If sperm quality is abnormal, the history should again be reviewed to determine if the dog has been sick recently or has received any drugs, especially anabolic steroids. Other recognized causes of abnormal sperm quality include inflammation of the scrotum or other factors that may be causing a high scrotal temperature, testicular neoplasia (ultrasonography of the testicles is recommended because many neoplasms of the testes are not palpable), trauma to the area of the scrotum, or brucellosis. However, most cases of low sperm quality in dogs are idiopathic.
The dog’s pituitary status can be investigated but is usually unrevealing. Luteinizing hormone and follicle-stimulating hormone are typically normal to high in dogs with abnormal semen quality because the degenerating testes are not able to provide the feedback mechanism to the pituitary. Because abnormal sperm quality may be induced by a recent transient disease or exposure to toxins, and spermatogenesis might resume, collections should be repeated about every 3 mo for ~1 yr before a definitive prognosis for breeding can be given.
Azoospermia is relatively common in dogs. It may be due to failure of the dog’s testicles to produce sperm, or to failure of the sperm to exit the testicles because of epididymal blockage or incomplete ejaculation. The ejaculate may be tested for the presence of alkaline phosphatase, which is secreted by the epididymis. A high value (>5,000 IU/L [very high in comparison with blood]) indicates fluid from the epididymis was collected. High alkaline phosphatase values in sperm-free fluid suggest that the testes are not producing sperm or that sperm transit is blocked between the testes and epididymides. Low values suggest epididymal blockage or failure of ejaculation; semen collections should be repeated, using a strong stimulus such as a bitch in estrus. The urinary bladder should be catheterized to determine if retrograde ejaculation is occurring; swab samples of the vagina of a bitch after natural mating may also be performed to determine if the dog is not ejaculating due to aversion to manual collection. Careful palpation and ultrasonographic examination should be performed to detect any abnormality of the epididymides or spermatic cords, such as absence or blockage of the epididymis.
The Merck Veterinary Manual