The Breeding Soundness Examination in Dogs and Cats
A breeding soundness examination, which should take place before any dog or cat is purposefully bred, is the opportune time for veterinary input regarding good breeding practices. Because of pet overpopulation, dog and cat breeding should be left to educated and responsible breeders, to whom potential purebred puppy and kitten clients can be referred. Breeding soundness means a dog or cat is free from heritable defects based on phenotype evaluations such as radiography (eg, elbow dysplasia), ultrasonography (eg, renal dysplasia, tricuspid dysplasia), ophthalmoscopy (eg, cataract), physical examination (eg, patellar luxation) or specific DNA testing when available (eg, progressive rod-cone degeneration). Several resources are available to veterinarians negotiating purebred dog and cat genetic recommendations.
A thorough history should be obtained concerning past health, medications, diet, and supplements (appropriate for breeding animals). Client handouts outlining potential problems associated with breeding (dystocia, mastitis, metritis, eclampsia, prostatitis, etc) are helpful. Potential breeding animals should be evaluated both historically (eg, atopic), physically (eg, severe brachycephalic syndrome, entropion, cryptorchidism), and mentally (eg, fearful, aggressive).
Female and male dogs both should undergo routine Brucella canis screening, even before the first breeding, because mucosal transmission does not require copulation (it can be transmitted through urine). Subsequently, females should be screened for brucellosis before each estrus when a breeding is planned; stud dogs should be tested annually and only bred to negative females. A negative Brucella canis screening test is reliable (unless <2–3 weeks after exposure); positive results warrant confirmatory (eg, agar gel immunodiffusion [AGID]) serologic evaluation, culture, or PCR, because false-positives are common. Clinicians should contact their commercial or academic laboratory for updated screening protocols.
Queens and toms should be screened for feline leukemia virus, feline immunodeficiency virus and feline infectious peritonitis as medically indicated. Female dogs and queens >5 years old should also have their general health assessed by performing a CBC, serum chemistries, and a urinalysis. Visits by a veterinarian to catteries experiencing reproductive difficulties are often rewarding, because basic husbandry problems can be discovered (light management, crowding, breeding management).
In dogs, in addition to a routine physical, the normalcy of the mammary glands and vestibulo-vaginal canal should be evaluated. Mammae may be asymmetric in number; nipples should not be inverted. A digital vaginal exam may only be possible when a female is in estrus; vaginoscopy provides the most thorough evaluation. Vestibulovaginal defects (strictures) can interfere with copulation and whelping, necessitating prebreeding repair or planned artificial insemination and elective cesarean section.
Vaginal strictures are congenital and occur as a septate strand or a circumferential band; they are commonly found at the vestibulovaginal junction, cranial to the urethral papilla. In some cases, the normal narrowing of the vestibulovaginal junction in the maiden (unbred) dog could be misinterpreted as a stricture; this should be reassessed when the dog is in estrus and vaginal tissues have become pliant. The heritability of such defects is unknown. Septate strands can be easily resected surgically, but circumferential strictures are difficult to resolve without episiotomy and major revision, and they tend to reform.
Routine prebreeding vaginal cultures are not advised because the vagina (and prepuce) normally harbors, as normal flora, a wide variety of bacteria, including beta-hemolytic streptococci and Mycoplasma spp.
Before an anticipated breeding, female dogs and cats should be in optimal body condition to improve conception rate and whelping outcome. A commercial diet adequate for all life stages is optimal. Breeders commonly advise skipping cycles between breedings; this is not optimal husbandry because the inevitable exposure to estrogen (queen) and progesterone (female dog, sometimes queen) during each estrous cycle promotes cystic endometrial hyperplasia and may result in pyometra. Female dogs and queens kept in optimal health can be bred sequentially and should then be ovariohysterectomized or ovariectomized when no further breedings are planned. Proper nutrition, housing, and exercise strategies for pregnancy and lactation should be outlined.
Female dogs should be currently vaccinated for core infectious diseases (canine distemper, parvovirus, adenovirus 2, and rabies). Other noncore vaccinations should be administered only according to good medical practice (appropriate for the dog’s age, health status, home and travel environment, and lifestyle). Queens should similarly be vaccinated appropriately (based on duration of immunity recommendations) for feline distemper, rhinotracheitis, and calicivirus. Vaccination against rabies virus, feline leukemia virus, and other noncore diseases should be done when indicated by good medical practice, based on risk factors associated with the cat’s age and husbandry. Unnecessary revaccination of female dogs and queens before breeding is not advised, because little improvement in immunity results. Vaccination during pregnancy is advised only when prior vaccination status is lacking or unknown and risk of exposure is high (eg, a shelter). In that case, the use of recombinant core vaccines is optimal.
The use of preventive medication for heartworm disease and internal and external parasite control (according to manufacturers’ labeling stating safety in breeding animals) during pregnancy and lactation is advised. Appropriate isolation of the pregnant female during the last third of pregnancy for infectious disease prevention is important (eg, avoiding exposure to canine herpesvirus in dogs and upper respiratory infections in cats). Client education concerning normal whelping and queening events and about the timely identification of dystocia is essential. Fetal and uterine monitoring systems developed for routine use in female dogs and cats improve neonatal survival, with reduced morbidity and mortality for the dam.
During a complete physical, particular attention is given to the genitalia. The penis should be fully extruded from the prepuce and examined. This may require sedation in toms. If hair accumulates around the base of the feline penis, it can prevent copulation and should be removed. Prostate size and symmetry should be assessed in dogs by simultaneous abdominal and rectal palpation or with ultrasonography; this is not generally necessary in cats because feline prostate disease is rare. Palpable abnormalities (pain or asymmetry) or semen abnormalities always warrant ultrasonographic evaluation of the prostate and further clinical testing as indicated (eg, urinalysis, urine culture). The testes and epididymides should be palpated carefully for symmetry and normalcy; abnormalities warrant ultrasonographic evaluation. The scrotum should be evaluated for evidence of acute or chronic dermatitis, which can impact fertility. A small amount of mucoid discharge at the preputial opening is normal in dogs. (Also see Reproductive Diseases of the Male Small Animal.)
Note: Medical procedures such as a physical examination, vital signs, venipuncture, or ultrasonography should be delayed if semen evaluation is planned, because libido will be impacted negatively.
Cryptorchidism, a common congenital defect in males, is diagnosed if both testes are not present in the scrotum at puberty; testicles normally descend into the scrotum by 6 weeks of age in the dog; scrotal testes should be present at birth in the cat but can be difficult to palpate due to their small size. Descent as late as 10 months has been documented in dogs. Unilateral cryptorchidism does not result in infertility. Bilaterally cryptorchid males are sterile but have normal testosterone levels.
In dogs, cryptorchidism is hereditary, and affected animals should not be bred. Both late descent and failure of descent are heritable. Both parents of affected individuals should be implicated as carriers. Because retained testes have a higher incidence of neoplasia and subsequent torsion, bilateral orchiectomy is recommended. Attempts at inducing descent with medical therapy using gonadotropins or testosterone have been unsuccessful and are not ethical. Orchiopexy is also considered unethical. Failure of one testis to develop (true monorchidism) is rare in dogs. Serum luteinizing hormone (LH) levels are high (>1 ng/mL) if a dog or cat is completely neutered; serum antimüllerian hormone (AMH) is positive in most postpubertal dogs and cats with any gonadal tissue. Examination for penile barbs in the tom cat also confirms the presence of testosterone.
A persistent penile frenulum in the dog prevents protrusion of the penis from the prepuce and thus copulation with a tie. Treatment is surgical. Chordee (deviation of the penis) is uncommon; these animals require assistance in breeding or may be bred via artificial insemination. Hypospadias (displaced urethral opening) is commonly associated with cryptorchidism. Some type of reconstructive surgery involving urethrostomy and penile amputation is usually necessary. Phimosis can be caused by stenosis of the preputial opening, which may be congenital or result from chronic inflammation (trauma or bacterial dermatitis). Any underlying cause should be treated and then, if necessary, the opening enlarged surgically. Most of these defects have a heritable component.
Ideally, a complete semen evaluation should be performed in male dogs intended for breeding and repeated at least annually in active stud dogs. Semen is readily collected from most dogs by manual stimulation; the presence of a teaser (estrual) female is advised to optimize results by improving libido. All equipment (artificial vagina, collecting tubes, pipettes, slides, and coverslips) should be room to body temperature, dry, and free of water and contaminants such as chemical disinfectants. The canine ejaculate consists of three fractions—the first and third are of prostatic origin, while the second is sperm-rich. Sperm production is related to testicular size, so large dogs should produce higher sperm counts than small dogs.
Semen evaluation should include an assessment of libido, total sperm count per ejaculate (normal in dogs is 200–400+ million; cats 6–16 million), sperm motility (normal >90% progressively motile, with moderate to fast speed), and morphology (>80% normal). The sperm count (sperm/mL) can be determined with a hemocytometer or by spectrophotometry. Sperm per ejaculate is calculated by multiplying the sperm count/mL by the total volume of semen collected.
Motility is evaluated in an unstained sample as soon as the sample is collected, ideally using clean prewarmed slides; although computer assisted semen analysis equipment is available, routine light microscopy (40X) is sufficient with practice. Several commercially available stains are suitable for morphology examination; eosin-nigrosin and Giemsa stains are used most commonly. Semen morphology slides are prepared and stained as any cytology sample; performing 100- to 200-cell counts noting morphologic defects is advised.
Primary defects occur during spermatogenesis, secondary defects occur during sperm transport and storage, and acquired defects occur secondary to inflammatory genitourinary disease, thermoregulatory disorders of the testes, heat stress, drugs, hematocele, hydrocele, and immune-mediated orchitis. Defects are also categorized as major or minor.
An adequate amount of the third fraction should be collected to ensure that the entire sperm-rich fraction has been acquired and to permit evaluation of the prostatic component, which should be clear (free of urine and cellular contamination). Subfertility or infertility should never be diagnosed based on one collection. Repeat collections >48 hours apart should be performed. If the sample is azoospermic, semen alkaline phosphatase can be measured in the ejaculate to assess whether the ejaculate was complete, because it is an epididymal marker.
Levels >5,000 mcg/dL indicate the ejaculate included the second, normally sperm-rich fraction. Levels <5,000 mcg/dL indicate either bilateral obstructive disease or libido problems preventing the release of the second fraction. Sperm function (eg, capacitation and acrosome reaction, zona pellucida binding) is not assessed with routine semen evaluation.
Collection of semen for evaluation is difficult in toms, unless the cat has been trained to ejaculate into an artificial vagina or electroejaculation equipment is available. Cats can be trained to ejaculate with manual stimulation in some instances, but training can take weeks to months. Chemical ejaculation using urethral catheterization under dexmedetomidine sedation or by fine needle aspiration of the testes for sperm cytology has been described. Nonspecific methods of evaluating a tom for spermatogenesis include evaluation of his urine for sperm or collecting a vaginal wash from the queen immediately after copulation, as spermatozoa disappear from the vagina within 1–2 hours of copulation.
To recover samples for analysis, warm saline (0.10–0.20 mL) is flushed into the vagina of the queen and aspirated, the sample is centrifuged, and the sediment examined (new methylene blue or routine hematologic stains are adequate). This should not be performed if the breeding is desirable, but only as a test of ejaculation. Breeding a questionable tom to a proven queen may be the most practical way to assess his fertility. Adequate coital contact to induce ovulation should be confirmed by measuring progesterone levels in the queen 1–2 weeks after breeding.
List of genetic testing laboratories for inherited diseases of dogs and cats from the University of Pennsylvania
Canine Inherited Disorders Database from the University of Prince Edward Island
Inherited Diseases in Dogs Database from the University of Cambridge
Canine Health Foundation from the American Kennel Club
Harmonization of Genetic Testing for Dogs from DogWellNet