Pamela A. Davol, 76 Mildred Avenue, Swansea, MA  02777-1620.
pdavol@labbies.com

Canine Reproduction

Part 4. Reproduction and the Male Dog

Normal Reproductive Development of the Dog (Male)

All embryos of mammals are programmed to become female. The presence of a single gene on the Y chromosome, however, will induce the development of the testes in an embryo destined to become male. Testis development is a critical part of male differentiation because this organ will secrete two substances required for the normal development of the male reproductive tract: mullerian inhibiting substance (MIS), which causes the mullerian ducts that would develop into the female organs of reproduction to regress; and testosterone, the male hormone that will stimulate the male organs of reproduction to develop from the wolffian ducts.  Conversion of testosterone to dihydrotestosterone will induce development of the prostate gland, the male urethra, the penis, and the scrotum. Subsequently, the testes descend into the scrotum and complete the development of the male reproductive system. Additional effects of testosterone will include the induction of other physical gender characteristics as well as male behavioral traits including mating drive and urine-marking of territory.

The male dog has two testes that are separated by connective tissue within the scrotum. Development of the spermatozoa (male germ cells) takes place in each testis. In the scrotum, a complex blood supply network and specialized muscular tissue maintains the temperature of the blood supplying the testes below normal body temperature. This facilitates optimal development (spermatogenesis) of the spermatozoa. At the onset of puberty, increased levels of lutenizing hormone (LH; a pituitary gonadotroph) induce the testes to produce testosterone, which will lead to the maturation of the spermatozoa. Once mature, the spermatozoa migrate from the testes to the epididymis (a compartment attached to each testis) where they are stored. One end of the epididymis tapers into the ductus deferens, the tube through which the mature sperm that are stored in the epididymis will pass to leave the scrotum. The ductus deferens leads into the prostatic urethra. During ejaculation, the sperm will be drawn out of the epididymis through the ductus deferens and will combine with semen, secreted by the prostate gland, in the prostate urethra before being expelled.

Evaluation of a Male's Soundness for Breeding

Successful breeding on the part of the male is dependent upon 1) his physical ability to copulate, 2) his drive to copulate (i.e. his libido), and 3) his ability to produce a normal semen sample. If any of these factors is compromised, then the likelihood of successful conception within the bitch may be greatly diminished or completely inhibited.

From a physical standpoint, proper nutrition and conditioning (exercise) are essential for assuring optimal performance and fertility in the male. Additionally, since breed-specific genetic disorders may not only impact upon the quality-of-life of future offspring but also compromise breeding performance of the male, males intended for breeding should receive a thorough physical examination to evaluate orthopedic, neurologic, endocrinologic, and genital systems prior to breeding.

In regard to semen quality, optimum fertility is not necessarily a factor of age of the dog, but appears to be more dependent on the stage of the sperm within the ejaculate (i.e. immature or aged sperm) or induced morphologic changes that occur in the sperm. Quality of the semen, therefore, is often more affected by factors other than age including degree of arousal, frequency of ejaculation, collection technique and sample handling. Since frequent ejaculation (daily collection of semen for 5 to 7 days) can cause a reduction in sperm output, studs in high demand may experience less than optimal fertility at certain times throughout their reproductive years. For this reason, it is recommended that sperm from valuable studs be collected and cryopreserved in sufficient quantities early in the male's career to ensure future availability. To this end, collection of semen on an "every other day" basis typically allows time for replenishment of sperm reserves.

Sperm Production in the Normal Male

Relationship between body weight, testis size and sperm count in adult dogs*

*Modified from Amann, RP: Reproductive physiology and endocrinology of the dog. In Morrow DA (ed) Current Therapy in Theriogenology 2. Philadelphia: WB Saunders, 1986, p. 536. (numbers are the mean ± SEM)

In the normal reproductive male, sperm production is directly related to testicular size. Sperm are stored in the extragonadal compartments of the epididymis and the ductus deferens. The amount of reserved sperm will depend on the frequency and interludes between ejaculations. Total sperm counts in a sexually rested male encompass sperm reserves plus daily sperm produced by the testes. Sperm reserves are reportedly depleted by once per day ejaculation for 5 to 7 days. Therefore, once reserves are depleted, total sperm number will be represented only by the daily production of sperm by the testes.

Collection of Semen for Artificial Insemination

Synbiotics of Malvern, PA and International Canine Semen Bank of Sandy, OR manufacture equipment for the collection of semen.   Typically, the device consists of a rubber collecting cone attached to a plastic centrifuge tube. Collection equipment should be sterile or disinfected prior to use. It is important to note that certain external factors such as temperature extremes, exposure to lubricants, and chemicals found in latex and plastic containers that may be used for sperm collection can adversely effect sperm and/or sperm motility. Therefore, stud owners who utilize homemade devices for semen collection should ensure that the materials used have no toxic side effects on spermatozoa; this also applies to methods for disinfecting the equipment.

At the time of collection, the male is introduced to a teaser bitch, either one in estrus or one in anestrus that has been treated with a topical pheromone (Eau d'Estrus by Synbiotics, Malvern, PA) and is allowed to sniff at the vulva. The individual doing the semen collection begins by providing manual stimulation to the penis, using brisk massage, through the prepuce (the outer fur-covered sheath). Once erection occurs, the prepuce retracts, at which point the collector can place the rubber collecting cone with attached tube over the enlarged penis. When the rubber collecting cone is in place, the collector should then tightly encircle the penis and collecting cone with the fingers to simulate the vulvar constriction of the bitch that occurs during the natural "tie."

The dog will ejaculate the semen in three fractions. The first fraction is the presperm fraction, which is a small volume of clear fluid. The second fraction is a cloudy, sperm-rich fraction. During ejaculation of this second fraction, the dog will usually thrust vigorously. Prior to ejaculating the third fraction, which consists of clear prostatic fluid, the dog will usually dismount and attempt to step over the arm of the collector. If the semen collected is to be stored rather than used for immediate insemination, it is important that the collector remove the tube containing the first two fractions prior to ejaculation of the prostatic fluid fraction. Prostatic fluid has been found to lead to a decrease in sperm motility if the spermatozoa are allowed to incubate with the prostatic fluid for any length of time prior to insemination. If insemination is to be performed immediately, the prostatic fluid may be collected with the first two fractions to yield a total semen volume that will be sufficient for insemination. For complete assessment of male reproductive function, however, it is often advisable to collect the prostatic fluid separately for the purpose of performing routine culture.

Semen Volume for Insemination:

When collection is complete, the rubber cone is gently removed from the penis. The dog should be monitored to ensure that the erect penis undergoes normal regression and returns to enclosure within the prepuce.

Handling and Evaluation of Semen

As with all body fluids, semen should be handled as a potentially biohazardous material. Many bacterial organisms that infect dogs may be transmitted to humans during collection of semen and therefore, semen presents a potential health risk. Accordingly, it is essential that the individual collecting and evaluating the semen practice basic "universal precautions" by considering the semen as potentially infectious and taking reasonable steps to reduce risks of infection (i.e. utilizing protective equipment such as gloves and eye goggles, frequent handwashing, proper disinfection or disposal of all contaminated equipment as biohazardous).

For evaluation of semen, the collection is divided into two parts: T1- consists of the presperm and sperm-rich fraction; and T2- consists of the prostatic fluid fraction.

In addition to the above, sediments from the T1 and T2 fractions should be examined for the presence of red blood cells, inflammatory cells, epithelial cells or bacteria which may indicate asymptomatic disorders of the male reproductive system. Semen cultures to identify bacteria are often difficult to interpret because of the numerous microorganisms that normally inhabit urethra and prepuce. However, significant numbers of bacteria in the sample may indicate presence of an infection. Additionally, prostatic fluid cultures may be helpful for identifying organisms associated with prostatitis or prostatic dysfunction. (Additional tests for evaluation of male reproductive dysfunction will be discussed in Part 5.)

Only samples assessed as normal by the above criteria should be used for insemination or stored for later insemination. Semen that is not used immediately for artificial insemination should be diluted with an extender that nourishes and protects the spermatozoa, chilled, and used within 24 hours. Long term storage of semen requires dilution with an extender containing a cryoprotectant and storage in liquid nitrogen.

Available Kits for Chilled and Frozen Semen

(For methods of artificial insemination please refer to Artificial Insemination in Canine Reproduction Part 1)