Male Reproductive System
Testes in domestic birds are normally paired and located cranioventral to the kidneys (Fig. 30-6). Like the ovaries, testes are smaller outside of breeding seasons and will increase markedly in size during breeding periods.
The microscopic appearance of an avian testis is similar to a mammalian testis in that it primarily consists of seminiferous tubules surrounded by an interstitium that contains Leydig cells. The process of spermatogenesis in the tubules is similar to that for mammals and is promoted by FSH and LH. However, unlike in mammals, spermatogenesis occurs in avian testes found normally within the body cavity, where they are maintained at normal core body temperature.The ductus deferens (deferent duct) conveys sperm from the testis to a raised papilla on the lateral aspect of the urodeum. Male birds do not possess accessory sex glands; the ejaculate is composed of sperm and scant additional secretions produced by the testes and the walls of the ducts.
On the ventral floor of the proctodeum of roosters and male turkeys there lies a copulatory organ, the phallus, which is nonprotrusible (i.e., does not form a protruding copulatory organ). The phallus has erectile tissue within it, and during copulation the engorged tissue forms a groove that conveys the ejaculate from the openings of the deferent ducts to the surface of the phallus. During the act of breeding, the proctodeum is everted and the phallus pressed against the vent of the female so as to facilitate the transfer of ejaculate.
Drakes and ganders (and, incidentally, male swans and ostriches) have a protrusible phallus that, when erect, is about 5 cm long. Its tip is spiraled and is introduced into the cloaca of the female during copulation.