Anatomical physiology of male dogs
Components of the canine spermatic cord include the ductus deferens, the testicular artery and vein, the lymphatics and nerves, and the cremaster muscle. The cremaster muscle and pampiniform plexus aid in thermoregulation of the testicles, which are maintained at 2~176 lower than basal body temperature. Sweat glands in the scrotum assist in lowering the scrotal
temperature through evaporation. The penis is a continuation of the muscular pelvic urethra and is attached to the ischiatic arch by two fibrous crura. It is composed of fibrous tissue and three cavernous sinuses: corpus cavernosum, corpus spongiosum penis, and corpus spongiosum glands. The accessory sex glands of the dog consist of only a well-encapsulated prostate gland that surrounds the pelvic urethra, and ampullary glands at the termination of the vas deferens in the urethra. The dog does not have seminal vesicles or bulbourethral glands.
The onset of puberty ranges from 5 to 12 months of age and is affected by breed, season, and nutritional and disease status.
Testicular growth is rapid at this time, and the seminiferous tubules begin to differentiate. The Sertoli cells from the blood-testis barrier, the tubules become hollow, and spermatogenesis
commences. This process is initiated by the secretion of LH from the anterior pituitary, which stimulates the production of testosterone by the interstitial, or Leydig's, cells. Secretion of follicle-stimulating hormone (FSH) by the anterior pituitary stimulates the production of other key hormones by the Sertoli cells, including inhibin, androgen binding protein, and estrogen. FSH stimulates spermatogenesis in the presence of testosterone, while inhibin and estrogen play a role in a feedback loop on the pituitary gland to decrease FSH production. Spermatogenesis in the dog is completed in 45 days, with subsequent
maturation of sperm occurring in the epididymis for approximately 15 days. Thus, the entire process from initiation of spermatogonial mitosis to the delivery of mature sperm to the ejaculate is 60 days.
A breeding soundness exam should be conducted to assess the probability of a male dog's successful production of offspring.
Factors affecting male fertility include libido, ability to copulate, testicular size, and quality and number of sperm produced.
Problems with libido may occur in dogs due to early weaning, isolation, or inherited abnormalities that suppress sexual behavior. Animals with poor hindlimb conformation or with trauma to the back or hindlimbs may be unable to properly mount the female. There is a positive correlation with the size of the testicles as measured by scrotal circumference
- Biology and diseases of dogs :
a number of sperm produced. Finally, the parameters used to assess the quality of sperm include motility, morphology, volume, and concentration. An ejaculate (5 ml) that contains approximately 500 million progressively motile sperm without significant morphological abnormalities (such as a kinked tail) is a good indicator of normal male fertility.
In general, erection, which involves muscular contractions and increased arterial blood flow to the penis, is controlled by the parasympathetic nervous system, whereas ejaculation is under sympathetic control. On mounting, the initial thrusting and ejaculation of semen last about 1 minute. The bulbous glands become enlarged, which lodges the penis in the female reproductive tract. The male then dismounts and brings one hind leg over the female, and the two continue to be joined "rear to rear," a position classically termed "the tie." Ejaculation of the accessory gland fluid continues for 5-30 minutes. The continued expulsion of prostatic fluid during the "tie" may serve to propel
Fertilization occurs in the oviduct and may occur as late as 8 days after coitus, because of the long lifespan of sperm in the dog. However, once ovulated, oocytes generally remain viable for only 12-24 hours. Therefore, the bitch should be bred prior to ovulation to ensure the presence of sperm for fertilization of live oocytes.