Chapter 72: Aspermia/Oligospermia Caused by Retrograde Ejaculation in Dogs

Web Chapter 72


Aspermia/Oligospermia Caused by Retrograde Ejaculation in Dogs




A retrograde flow of small quantities of spermatozoa into the bladder is a normal event. This may occur during ejaculation or sexual rest and has been documented in many species, including the bull, ram, cat, dog, and human. Because testicular sperm production is a continuous event, sperm leave the testis at a constant rate and move through the caput and corpus epididymis as a result of rhythmic contractions of the smooth-muscle epididymal wall. Although the cauda epididymis is normally quiescent, occasional smooth-muscle contractions at this level promote voiding of spermatozoa and epididymal fluids into the urethra during periods of sexual rest, which explains the common finding of spermatozoa in the urine sediment of humans and domestic male animals. In dogs examination of the urine sediment has been suggested as a way to establish occurrence of spermatogenesis.


A retrograde flow of large quantities of spermatozoa into the bladder is an abnormal event, which may occur during ejaculation as a result of a partial or complete absence of bladder neck contraction during semen expulsion. When this happens, the bladder becomes the least resistant pathway for seminal fluids coming from the urethra. The ejaculate is scant or absent, and spermatozoa can be retrieved in large quantities from the bladder. After erection and pelvic thrusting, a normal dog produces an ejaculate composed of 0.5 to 2.5 ml of presperm and sperm-rich fraction and 4 to 45 ml of prostatic fluid fraction, depending on testicular volume. A complete lack of ejaculate or production of minute quantities of ejaculate may indicate that semen was diverted totally or almost totally from its normal ejaculatory path and flowed into the bladder. Retrograde ejaculation is defined as a retrograde flow of the majority of or all the semen into the bladder, resulting in no semen (aspermia) or minute quantities of semen (oligospermia) ejaculated antegrade.


Aspermia in the dog may be caused by sexual immaturity, pain, psychologic factors; drug therapy; diseases of the reproductive tract, such as Brucella canis and Pseudomonas aeruginosa infection; or sympathetic neuropathy either idiopathic or secondary to diabetes mellitus or spinal cord injury. Oligospermia in the dog may be idiopathic or caused by season; unilateral Sertoli cell tumor; prostate disease, orchitis, and epididymitis caused by B. canis, Escherichia coli mycoplasma, and other aerobic organisms; immune-mediated orchitis; or use of drugs such as steroids, chemotherapeutic agents, ketoconazole, and gonadotropin-releasing hormone agonists/antagonists. An oligospermic ejaculate is characterized by a low number of spermatozoa diluted in a small quantity or in a normal quantity of prostatic fluid. However, presence of a normal quantity of prostatic fluid in the ejaculate generally rules out failure of bladder neck closure. Therefore retrograde ejaculation should be suspected whenever an aspermic or oligospermic (0.1 to 0.3 ml total volume) ejaculate is produced after normal erection and pelvic thrusting.



Normal Antegrade Ejaculation


The ejaculatory process consists of three distinct events: seminal emission (the deposition of seminal fluid originating from the vasa deferentia and the prostate into the prostatic urethra), bladder neck closure (caused by contraction of the dorsal segment of the bladder neck), and seminal expulsion or ejaculation (the passage of seminal fluids through the urethra followed by their expulsion through the external urethral orifice). Once erection is achieved, peristaltic contractions in the epididymis and vas deferens caused or increased by oxytocin start to convey spermatozoa and seminal plasma into the prostatic urethra, causing an increase in urethral pressure. Such an increase (helped by contraction of the smooth muscle cell component of prostatic lobules) forces prostatic fluid into the prostatic urethra, which in the adult male dog has a rich elastic layer in the submucosa and is almost devoid of smooth muscle. Further increase in intraurethral pressure occurs when the erectile tissue of the urethra expands, thereby reducing the urethral lumen. When the intraluminal pressure of the vasa deferentia and prostatic urethra reaches maximum, the striated musculature of the pelvic urethra relaxes, which allows expulsion of seminal fluid outside through the pelvic and penile urethra. Seminal emission is powered by recoil of elastic fibers in the prostatic urethra. At this point a striated urethral muscle peristaltic wave cycle sets in motion, which completes the ejaculatory process.


The bladder neck plays an important role during seminal emission and seminal expulsion, preventing a retrograde flow of semen into the urinary bladder. During the ejaculatory process the canine bladder neck shows periods of intense contractile activity followed by phases of relaxation. The duration of each relaxation phase decreases gradually until a continuous contractile momentum of the dorsal segment of the bladder neck (the ventral segment of the canine bladder neck is involved primarily with continence and voiding) occurs toward the end of the ejaculatory process. When the dorsal segment of the bladder neck is relaxed (during sexual rest and in between urethral muscle peristaltic contractions early in the ejaculatory process), semen may flow back into the urinary bladder following the least resistant pathway. If the bladder neck contracts at ejaculation, the urethra becomes the least resistant pathway through which semen is propelled outside.


The ejaculatory process is coordinated by sympathetic and parasympathetic neural activity. The brain facilitates or inhibits sexual function by mediating and integrating reproductive motivation and reproductive behavior with other types of social behavior, whereas the spinal cord integrates visceral and somatic stimuli, evoking the reflexes of erection and ejaculation. Spinal reflexes occurring during the ejaculatory process in the dog are listed in Web Table 72-1.


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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Chapter 72: Aspermia/Oligospermia Caused by Retrograde Ejaculation in Dogs

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