Normal Reproductive Development of the Dog (Male)
All embryos of mammals are programmed to become female.
The presence of 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
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 MaleRelationship between body weight, testis size and sperm count
in adult dogs*
Body weight (lb)
total scrotal testes width (mm)
semen volume/ejaculate (ml)
daily sperm production (106)
semen conc (106/ml)
total sperm (109)
Extragonadal sperm reserves
-based on 7 days sexual rest
*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 ±
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
International Canine Semen Bank of Sandy, OR manufactures
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)
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.
Weight of bitch
10 pounds (4.5 kg) or less
10 to 50 pounds (4.5 to 22.7 kg)
3 to 5 ml
pounds (22.7 kg) or more
5 to 8 ml
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.
cream to white color
- clear or only slightly cloudy (suggests absence of sperm or low sperm count)
- pink (blood)-tinged
(suggests prostatic disease or traumatic collection)
(suggests contamination of semen with urine)
Clear (as water)
(suggests prostatic disease)
varies according to breed
varies according to length of collection time
(percent of sperm that move in a straight path)
abnormal, reduced or absent motility (asthenozoospermia)
³ 250 million (greater in
£ 100 million (oligozoospermia)
³ 200 with normal morphology
£ 50 % with normal morphology (teratozoospermia)
< 10,000 bacteria/ml
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.