Veterinary Andrology and Reproductive Techniques

SCROTUM AND TESTIS

• The scrotum is a bilobed sac/pouch (derived from the skin and fascia) in which testicles are located.
• The scrotum in all the domestic animals is located in between thighs except in boar and cat. In boar and cat the scrotum is located caudal to thighs and caudal and ventral to ischiatic arch.
• The testis is fixed to the scrotum by means of scrotal ligament which is attached to its caudal end near the tail of the epididymis.
• The scrotum is generally devoid of hair except in cat, sheep and goat. Different layer of tissues that are present in between the scrotal skin and the testis proper are as follows.

Skin

• The outer most layer contain sweat and sebaceous glands.

Tunica dartos layer

• It is the layer present below the scrotal skin and is composed of smooth muscle fibers with fibrous and elastic connective tissue.
• Tunica dartos layer surrounds both the testes and forms a medial septum which divides the scrotum into two halves.

Loose connective tissue layer is present under the tunica dartos layer.

Tunica vaginalis layer

• It is present under the loose connective tissue layer. This layer is an extension of peritoneum passing through the abdominal wall at the inguinal canal.

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The vaginal process layer is composed of

• superficial layer called tunica vaginalis communis, which corresponds to the parietal peritoneum of the abdominal cavity. It covers the scrotal cavity.
• deeper layer called tunica vaginalis propria, which corresponds the visceral layer of peritoneum of the abdominal cavity. It covers the testis and epididymis.
• The tunica vaginalis secretes a lubricating fluid.
• Tunica albuginea layer is a dense, thick connective tissue layer present beneath the visceral layer of the tunica vaginalis.
• Extensions of the tunica albuginea penetrate the testicular parenchyma to join at mediastinum. These fibrous septa divide the testicular parenchyma into lobules. The lobules are having the highly coiled seminiferous tubules. About 75% of the testicular mass is composed of seminiferous tubules. The length of the seminiferous tubules estimated in different species is as follows

S.No.	Species	Length
1	Bull	5000 m
2	Ram	4000 m
3	Boar	6000 m
4	Dog	150 m
5	Cat	25 m

• The seminiferous tubules are lined by germinal epithelium and produce spermatozoa. The seminiferous tubules join the rete testes through straight tubules (the tubuli recti). From rete testes the sperm cells are passed to efferent tubules (6 to 24 in number) and then to head of the epididymis.
• In stallion there is no mediastinum testis and the collecting tubules join the efferent tubules.
• The testis is located in the scrotal pouch and is held by its tunics and the spermatic cord.
• The spermatic cord is composed of the following:
  • Spermatic artery
  • Spermatic vein
  • Internal cremaster muscle
  • Lymphatic vessels
  • Autonomic nerves
  • Vas deferens
  • Tunica vaginalis propria
• The consistency of the testis is usually turgid.
• The testicular parenchyma is usually brown in color and bulges on section.

Characters	Bull	Stallion	Ram	Boar	Dog	Cat
Shape	Oval	Oval	Oval	Oval	Round to oval	Round to oval
Length	10-15 cm	7.5-12.5 cm	7.5-11.5 cm	10-15 cm	2-4 cm	1.2-2 cm
Diameter	5-8.5 cm	4-7 cm	3.8-6.8 cm	5-9 cm	1-2.5 cm	0.7-1.5 cm
Weight	200-500 gm	200-300 gm	200-400 gm	600 gm	7-15 gm	0.7-1.5 cm
Plane	Vertical	Horizontal	Vertical	Vertical	Oblique	Oblique

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• In bulls - head of the epididymis is dorsal and tail ventral to the testis.
• In stallions - the head of the epididymis is cranial and tail caudal to the testis. The appendix testis is present at cranial pole of testis. It is remnant of paramesonephric duct.
• In Rams - head of the epididymis is dorsal and tail ventral to the testis. Appendix testis is rarely present
• In boars - the head of the epididymis is ventral and tail dorsal to the testis.
• In dogs - the head of the epididymis is cranial and tail caudal to the testis
• The bull, dog and boar will have large internal inguinal ring and small inguinal canal
• The stallions will have small internal inguinal ring and large inguinal canal
• Blood supply – internal spermatic artery which is a branch of abdominal arota.
• Nerve supply – internal spermatic nerve

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