THE NORMAL CANINE EJACULATE

Canine ejaculation may be elicited by manual stimulation of the penis in the presence of an estrous teaser bitch. Application to the distending penis of a latex artificial vagina (Nasco, Fort Atkinson, WI, USA) connected to a 12-14 cc calibrated plastic centrifuge tube is recommended to simulate normal copulation. The presence of an estrous teaser bitch has been demonstrated to result in a better quality of semen collected by manual stimulation of the male dog. Dog semen is ejaculated in three fractions: (i) the acellular pre-sperm fraction (0.5 to 5.0 cc), which may originate in the prostate; (ii) the sperm-rich fraction (1.0-4.0 cc) which originates in the testes and epididymis; and (iii) the prostatic fluid fraction (2.5-> 80 cc) which also is acellular and originates in the prostate.

DEFINITION OF AZOOSPERMIA

Azoospermia is ejaculation of seminal fluid that does not contain spermatozoa. Because normal volume of the complete ejaculate in the normal dog may range from only a few cc to more than 100 cc, volume of the ejaculate of the azoospermic dog usually is not contributory to localizing site or cause of the azoospermia.

LOCALIZING SITE OF THE CAUSE OF AZOOSPERMIA

Causes of azoospermia in the dog are listed in Table 1. Localization of the cause of azoospermia in the dog is made by general physical examination and by measurement of alkaline phosphatase in the seminal fluid.

Physical examination should focus on presence of two testes of normal size and position in the scrotum. Causes of azoospermia (Table 1) that may be detected on physical examination include scrotal/inguinal hernia, cryptorchidism and abnormalities of sexual differentiation if testes are small or abnormally positioned. In addition, evidence of testicular injury, infection or neoplasia (swelling, bruising, pain) or of testicular atrophy (spermatogenic arrest, autoimmune orchitis, end stage testes) may be detected at physical examination.

Alkaline phosphatase (AP) in canine seminal plasma arises predominantly from the cauda epididymis, making it a useful epididymal marker when evaluating azoospermia. Seminal plasma AP concentration in a complete ejaculate without tubular obstruction is > 5,000 U/L. Seminal plasma AP concentration in the first fraction of semen (or in the incomplete ejaculate) may be less than 100 U/L. Seminal plasma AP concentration in the ejaculate of dogs with bilateral epididymal cysts or sperm granulomas are generally less than 5,000 U/L, depending on location of the lesion. Seminal plasma AP concentration greater than 5,000 U/L in an azoospermic semen sample from the dog usually indicates presence of a complete ejaculate in primary testicular failure.

INCOMPLETE EJACULATION

The main differential diagnosis for dogs with normal physical examinations and very low (< 100 U/L) seminal plasma alkaline phosphatase is incomplete ejaculation. Some dogs, and especially those that are experienced breeders, will not ejaculate completely unless they are in the presence of a peri-ovulatory estrous bitch. Diagnostic plan for these dogs is to collect several more ejaculates in the presence of such a bitch, and to be sure that the semen collection continues until prostatic fluid in the third fraction (often signaled by rhythmic rectal contractions at the end of the collection) is identified.

DIAGNOSIS AND TREATMENT OF PRIMARY TESTICULAR FAILURE

The prognosis for almost all dogs with azoospermia and seminal plasma AP greater than 5,000 U/L is poor. In young dogs, karyotype may be instructive in ruling out an abnormality of sexual differentiation (such as 79, XXY), but usually will not present a treatment option. Reversible causes of azoospermia in this category include injury, infection and testicular neoplasia, so culture of the semen and testicular ultrasound, looking for a tumor that could be removed, are indicated. Testicular biopsy may or may not reveal etiology of the azoospermia.

DIAGNOSIS AND TREATMENT OF BILATERAL OUTFLOW OBSTRUCTION

The diagnostic approach to a dog with azoospermia and seminal plasma AP ranging from 1,000 to 5,000 U/L is epididymal ultrasound, and possible epididymal exploration, looking for cysts or sperm granulomas. Culture of the seminal plasma for aerobes, anaerobes and mycoplasma is recommended in case an infectious cause of a sperm granuloma can be identified. Prognosis for future fertility usually is poor.

Table 1. Causes of Azoospermia in the Dog and Diagnostic Tests of Choice

(Reprinted with permission from Johnston, S.D., Root Kustritz, M.V., Olson, P.N.: Clinical approach to infertility in the male dog. In Canine and Feline Theriogenology, W.B. Saunders Co., Philadelphia, PA, 2001, p 377.)

REFERENCES

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2.  Frenette, G., Dube, J.Y., Tremblay, R.R.: Origin of alkaline phosphatase of canine seminal plasma. Arch. Androl. 16:235-241, 1986.

3.  Johnston, G.R., Feeney, D.A., Johnston, S.D., and O'Brien, T.D.: The ultrasonographic features of canine testicular neoplasia: 16 cases (1980-1988). J. Am. Vet. Med. Assn. 198: 1779-1784, 1991.

4.  Johnston, S.D.: Premature gonadal failure in domestic dogs and cats. J. Reprod. Fertil. Suppl. 39: 65-72, l989.

5.  Johnston, S.D., Root Kustritz, M.V., Olson, P.N.: Clinical approach to infertility in the male dog. In Canine and Feline Theriogenology, W.B. Saunders Co., Philadelphia, PA, 2001.

6.  Majeed, Z.Z.: Segmental aplasia of the wolffian duct: report of a case in a poodle. J. Small Anim. Pract. 15:263-268, 1974.

7.  McEntee, K.: Efferent ductules, epididymis, and deferent duct. In Reproductive Pathology of Domestic Animals, Academic Press, San Diego CA, 1990, pp 307-332.

8.  Meyers-Wallen, V.N.: Inherited abnormalities of sexual development in dogs and cats. In Recent Advances in Small Animal Reproduction, P.W. Concannon, G. England, J. Verstegen, (ed), International Veterinary Information Service, Ithaca, NY, 2001.

9.  Nie, G.J., Johnston, S.D., Hayden, D.W., Buoen, L.C., Stephens, M.: Theriogenology Question of the Month [A 79,XXY chromosome complement in a dog with seminiferous tubule dysgenesis]. J. Amer. Vet. Med Assn. 212:1545-1547, 1998.

10. Olar T.T., Amann R.P., Pickett, B.W.: Relationships among testicular size, daily production and output of spermatozoa, and extragonadal spermatozoal reserves of the dog. Bio. Reprod. 29: 1114-1120, 1983.

11. Olson, P.N.: Clinical approach for evaluating dogs with azoospermia or aspermia. Vet. Clin. No. Amer. 21:591-608, 1991.

12. Olson, P.N., Schultheiss, P., Seim, H.B.: Clinical and laboratory findings associated with actual or suspected azoospermia in dogs: 18 cases (1979-1990). J. Am. Vet. Med. Assoc. 201:478-482, 1992.

13. Root, M.V., Johnston, S.D., and Olson, P.N.: Concurrent retrograde ejaculation and hypothyroidism in a dog: Case report. Theriogenology 41:593-600, 1994.