Avian Male Reproductive Tract - Anatomy & Physiology

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Testes

• Bean-shaped, paired
• Lie near the cranial pole of the kidney
• Medially, they lie close to the aorta and caudal vena cava.
• Each testical suspended by a short mesochorium and surrounded medially by the abdominal air sac.
• Left tends to be larger than right in immature birds.
• Dimentions increase rapidly with sexual activity.
• In the non-breeding season, testes shrink to almost nothing and become hard to visualize.
• Dormant testes light brown/yellow in colour, turn white when sexually active.
  • In some psittacine species, immature or dormant testes may appear black due to melanocytes located in the interstitium.
• Semniferous tubules produce sperm from the epithelium.
• Interstitial Leydig cells lie between semniferous tubules.
• Tunical Albiguinea thinner than in mammals.
• No Pampiniform plexus.
• Epididymis is small and can be considered absent. Sperm maturation occurs in the Vas Deferens.
• Vas Deferens closely associated with the Ureter in the dorsomedial midline coelom, distinguished by its zig-zag appearance.
• Vas Deferens enters dorsal wall of the Urodeum.
• No accessory sex glands.

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Phallus

• Most birds lack a true phallus.
• Analogue of the mammalian penis.
• Consists of a small median tubercle flanked by a pair of large, lateral phallic bodies.
• When present, the avian phallus is soley reproductive and becomes engorged by lymph fluid instead of blood during erection.
• Owing to the lack of accessory sex glands, avian semen has low volume.
  • Some lymph may contribute to the seminal fluid.
• Sperm remains viable in the female tract for much longer than in mammals.
  • May survive for 5-6 days.

Absence of Phallus

• Psittacines, Passerines, Pidgeons and birds of prey all have no phallus.
• Copulate by transferring semen from the everted Cloaca directly into the female oviduct.

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Non-Protrusible Phallus

• Rudimentary non-protrusible phallus is seen in male Turkeys and Chickens.
• Lies on the ventral lip of the vent.
• Consists of a small medial tubercle intimately associated on each side with lymphatic folds and vessels.
• When erect with lymph, the phallus develops a median groove.
  • Median groove permits passage of ejaculate down into the everted female oviduct.

Protrusible Phallus

• Ratites and Anseriformes
• Elongated, capable of true intromission into the female cloaca.
• Distal end lies enclosed in a cavity on the floor of the cloaca and becomes engorged with lymphatic fluid.
  • Anseriformes have a curved, fibrous phallus that conveys semen via a spiral groove.