The male reproductive system in dogs and tomcats, while sharing fundamental functions, exhibits distinct anatomical and physiological differences crucial for understanding reproduction in these species. This article delves into the comparative aspects of their reproductive tracts, focusing on the production of spermatozoa, secretion of vital fluids, and hormonal regulation.
Anatomy and Function of the Male Reproductive System
The primary roles of the male reproductive system are the continuous production of spermatozoa through spermatogenesis, the secretion of fluids that support sperm viability and transport, and the production of testosterone, essential for male secondary sexual characteristics and behavior. While the general anatomy of the dog (canid) and tomcat (felid) reproductive systems are similar, notable variations exist, as illustrated in Figures 1 and 2.
Testis and Scrotum
A pair of testes are responsible for spermatogenesis, a process that requires a temperature below 40°C. In both species, the testes are housed outside the body cavity within the scrotum, a pouch of pigmented, sparsely furred skin. The location of the scrotum differs: in dogs, it lies between the upper thighs, whereas in tomcats, it is positioned ventral to the anus, near the ischial arch.
The scrotum’s temperature regulation is managed by the Dartos muscle. This muscle contracts in cold weather, drawing the testes closer to the body for warmth, and relaxes in warm weather, allowing them to descend and cool.
Inside the scrotum, the majority of the testicular tissue comprises coiled seminiferous tubules. These tubules are lined with spermatogenic cells, responsible for sperm formation, and Sertoli cells, which provide nutrients to sperm and secrete small amounts of estrogen. Interstitial cells, or Leydig cells, located between the seminiferous tubules, are the primary producers of testosterone.
The seminiferous tubules converge to form the epididymis, a long, coiled tube adjacent to the testis. The epididymis, particularly its caudal part (cauda epididymis), is where sperm undergo final maturation and are stored before ejaculation. From the cauda epididymis, the deferent duct (vas deferens) carries sperm out of the scrotum, through the inguinal ring, and into the peritoneal cavity.
The testis is enveloped by the tunica vaginalis, a double layer of peritoneum that also surrounds the spermatic cord. This cord contains the testicular artery, vein, nerves, and the deferent duct. The testicular artery forms the pampiniform plexus, a network of arterioles that cools the blood before it reaches the testicular tissue, ensuring optimal conditions for spermatogenesis. The cremaster muscle, also within the spermatic cord, works with the Dartos muscle to adjust scrotal temperature.
Deferent Duct
The deferent duct, or vas deferens, is a direct continuation of the cauda epididymis. It travels within the spermatic cord and enters the peritoneal cavity via the inguinal ring, an opening in the abdominal wall muscles. The deferent ducts from each testis merge with the urethra within the prostate gland.
Urethra
The urethra serves as a common passageway for both the urinary and reproductive systems, extending from the bladder’s neck to the penis tip. In dogs, the urethra is divided into a longer pelvic part and a penile part. Conversely, tomcats have a shorter preprostatic urethra connecting the bladder to the prostate gland. Their penile urethra is also shorter, ending at the ischial arch with an opening directed caudally. This anatomical position in tomcats is linked to their scent-marking behavior.
Accessory Glands
Both dogs and cats possess a prostate gland near the bladder neck. Additionally, tomcats have bulbo-urethral glands near the penis tip. These glands contribute secretions that increase ejaculate volume, aid in propulsion, neutralize urethral acidity from residual urine, and create a favorable environment for sperm.
Penis
The penis is composed of cavernous erectile tissue (corpus cavernosum penis) surrounding the urethra. During sexual excitement, this tissue engorges with blood, enabling the penis to be introduced into the female reproductive tract.
Dog Penis: The dog’s penis has a root attached to the ischial arch by muscular crura. It then forms the body, extending between the thighs, and culminates in the glans penis. A small bone, the os penis, is embedded within the glans penis, dorsal to the urethra. This bone provides rigidity, aiding initial vaginal entry. The urethra passes through a bony tunnel within the os penis, which can be a site for urethral calculi blockage.
Tomcat Penis: The tomcat’s penis has a shorter length of erectile tissue. The bulbo-urethral glands open into this region. A bony os penis is located ventral to the urethra, which is narrow in this area and prone to blockage by struvite crystals. The glans penis is covered in backward-pointing barbs. These barbs cause pain upon withdrawal after coitus, initiating a reflex ovulation in the queen approximately 36 hours later, as queens are induced ovulators.
Prepuce
The prepuce is a protective sheath covering the penis when relaxed. It consists of hairy skin externally and a mucous membrane internally, continuous with the urethra and equipped with lubricating glands. Inflammation of the prepuce, known as balanoprosthitis, results in a greenish discharge.
Author: Victoria Aspinall bvsc mrcvs
