Also see Infertility in Dogs and Cats and Infertility in Poultry.
Interaction of the CNS, hypothalamus, pituitary gland, gonads, and their target organs results in finely coordinated sequences of physiological events that lead to estrus and ovulation in females and to ejaculation of fertile semen in males. For optimal results, ovulation and deposition of semen into the female genital tract must be closely synchronized. Failure of any single functional event in either sex leads to infertility or sterility.
The ultimate sign of infertility is failure to produce offspring. In polytocous species, a subnormal number of offspring also constitutes infertility. In females, infertility can be due to any of the following:
failure to cycle
aberrations of the estrous cycle
failure to conceive
prenatal or perinatal death of the conceptus
infections
Major infertility problems in males can be due to any of the following:
disturbances in the production, transport, or storage of spermatozoa
aberration of libido
physical problems leading to a partial or complete inability to breed
Most major infertility problems have a complex etiology, and several factors, singly or in combination, can result in reproductive failure. Pathogenesis may be equally complex.
Diagnostic Approach to Infertility in Animals
Because the female bears the offspring, she reflects either success or failure of reproduction. However, the first step in diagnosing infertility, regardless of the clinical presentation, is to establish the etiological role of both the female and the male. In addition, each point of human involvement in the reproductive process, such as observation for estrus, preservation of semen, and insemination methodology, is a potential source of error. Such human errors can be detected or excluded by assessment of performance, with the main emphasis on techniques and procedures and their adequacy and quality.
Diagnostic methods used to test the anatomical and functional soundness of both sexes include the following:
signalment
complete patient history
clinical examination
diagnostic aids, such as:
endoscopy
ultrasonography
laboratory tests (eg, hormone assays; microbiological, cytological, and serological tests; cytogenetic examination; genetic testing; and semen evaluation)
Choice of diagnostic method(s) is determined by the species, size, and temperament of the patient. Determination of the type and extent of laboratory tests used is guided by patient history and information gained during clinical examination. In each case of reproductive failure, the diagnostic plan should provide evidence to establish the role of the female, the male, and the breeding management program.
Reproductive problems are seldom accompanied by alarming clinical signs of disease. Furthermore, there often is a time interval between when failure occurs and when it becomes apparent—for example, the interval between unsuccessful service and return to estrus, or the interval between fetal infection and subsequent abortion. This lag period may allow recovery, yielding negative results on examination or diagnostic testing. Interpretation of results must also account for species differences and, in species with a seasonal reproductive pattern, the fact that infertility may be physiological during certain parts of the year.
