The male reproductive organs in the domestic fowl consist of two testes, each with a deferent duct that leads from the testes to the cloaca. Fowls do not have a penis found in other animals. The testes are bean shaped bodies located against the backbone at the front of the kidney. Their size is not constant and they become larger when the birds are actively mating. The left testes are often larger than the right. On the inside of each as they are located in the body cavity is a small, flattened area that is believed to correspond to the epididymis of mammals. The deferent duct starts at this flattened area.

Deferent duct

The deferent duct transports the sperm from the testes where they are formed to the cloaca from which they enter the oviduct of the female when mating. The deferent duct enters a small pimple like structure in the cloaca. This structure represents the mammalian penis and is much larger in ducks to form a penis like organ. The deferent duct is quite narrow at first but widens as it approaches the cloaca.

Testes and sperm

In the testes very twisted tubes called seminiferous tubules are found. It is in these tubules that a special process of cell division called meiosis and transformation produces the sperm. The sperm carry half of the total chromosomes required to produce an embryo. The mother provides half the other. One cubic millimetre of the fluid called semen produced by the male contains on average 3-5 million sperm. Under a microscope the sperm of the fowl will be seen to have a long pointed head with a long tail. The testes also produce hormones called androgens that influence the development of what are called secondary sex characteristics such as comb growth and condition, male behaviour and mating.