The most common cause of infertility in dogs and cats is related to husbandry problems (timing, techniques, male selection). Breeding with a proven fertile male must occur at the optimal time for the female. Infectious, anatomic, metabolic, and functional problems associated with infertility are seen less frequently.
The only confirmed infectious cause of infertility in female dogs is brucellosis. This highly contagious disease caused by Brucella canis results in abortion and infertility in female dogs and infertility associated with orchitis and epididymitis in males. Neutered dogs can be infected and display discospondylitis, osteomyelitis, uveitis, and lymphadenitis. A rapid slide agglutination test (RSAT) kit to detect serum antibodies is commercially available. If the RSAT is negative, the female is presumed to be Brucella-free unless exposure was <2–3 weeks previously; if positive, further confirmatory laboratory testing is indicated (eg, AGID, PCR, 2-mercapto-ethanol RSAT, culture).
In cats, infectious causes of infertility include:
These may cause abortion, neonatal death, fetal resorption, and apparent infertility. Less common infectious causes of infertility and abortion include toxoplasmosis, leishmaniosis, minute parvovirus, cryptosporidiosis, and feline herpesvirus.
Anatomic causes of infertility include acquired and congenital problems. Fibrosis of the oviducts or uterine horns, probably a result of inflammation after infection or trauma, leads to infertility. Diagnosis is via laparotomy with dye studies. There is no reliable treatment, although microsurgery may be attempted. Similarly, bilateral obstruction of the sperm ducts can cause azoospermia and infertility. High environmental temperature and excessive conditioning resulting in increased body temperature can induce either temporary or permanent azoospermia. Kennel or cattery management should allow for breeding males to remain cool during the summer. Scrotal dermatitis can have the same result. Disorders of sexual differentiation result in infertility (eg, hermaphroditism, pseudohermaphroditism).
Metabolic causes of infertility, other than in severely ill individuals, are rare. Hypothyroidism has no effect on male libido or semen quality. Hypothyroid female dogs might not cycle or have increased abortion rates, or neonatal survival may be poor.
Estrous cycle abnormalities can cause infertility. Prolonged anestrus may be congenital or acquired. Some large breeds of dogs may not have their first estrus until they are ≥2 years old, and some individuals and some breeds typically have only one estrous cycle each year. Congenital forms of anestrus may be due to lack of function of the hypothalamic-pituitary axis or ovarian dysgenesis.
The diagnosis of congenital anestrus is based on the age of the animal and exclusion of all other possible causes (including chromosomal defects, endocrine disorders, and previous oophorectomy). Because cyclicity in queens is determined by photoperiod, lighting conditions should be appropriate for several months before congenital anestrus is diagnosed and exogenous hormones are administered. One reported method to induce estrus in cats is FSH at 2 mg/cat, IM, once daily until signs of estrus appear (not administered for >5 days).
Acquired anestrus may result from previous oophorectomy, exogenous hormonal treatment (including glucocorticoids), profound hypothyroidism, or ovarian disease (cysts or neoplasia). Diagnosis is based on history, physical examination, biochemical evaluation, ultrasonography, and laparotomy.
Prolonged estrus may be caused by ovarian cysts that produce estrogen, functional ovarian tumors, or exogenous estrogens (including human transdermal hormone replacement therapy). Exogenous hormones should be discontinued. Laparotomy with histopathology is usually indicated, because medical attempts at inducing ovulation (human chorionic gonadotropin, FSH, GnRH) are usually unrewarding. Prolonged diestrus can result from luteal cysts or a progesterone-producing tumor in the ovary. Medical manipulation with prostaglandins is usually unrewarding, and ovariectomy with histopathology is indicated. Biopsy of the endometrium may be indicated after longterm progesterone exposure; the induction of endometrial hyperplasia could result and could also result from the biopsy.
Prostatitis (bacterial) can be subclinical and contribute to subfertility and infertility in dogs, primarily by impacting semen quality. Benign prostatic hyperplasia does not affect fertility but results commonly in hemospermia, a benign condition except for making semen cryopreservation unsuccessful. Cystic benign prostatic hyperplasia is nonmalignant, with hemospermia resulting, but may predispose the dog to bacterial colonization of the cysts and result in septic prostatitis. Benign prostatic hyperplasia and cystic benign prostatic hyperplasia can be treated with finasteride (1–5 mg, PO, daily) with some success.
Testicular neoplasia, sometimes functional and producing estrogen, can cause infertility. Unilateral gonadectomy of the affected testis may allow the other testis to regain its ability to produce sperm, but the prognosis is guarded.