The male fowl has two testes that are situated along its back. These never descend into an external scrotum, as do those of other farm animals. Some male chickens are "caponized" or castrated (surgical removal of the testes) to make them fatten more readily. The operation is relatively simple and requires no stitches to close the incision.
A testis consists of a large number of very slender, much convoluted ducts, from the linings of which the sperm are given off. These ducts appear in groups separated by delicate membranes that extend inward from a parent membrane that surrounds the testis. They all lead eventually to the ductus deferens, a tube that conducts the sperm to a small papilla; together, the two papilla serve as an intermittent organ. They are located on the rear wall of the cloaca.
The rooster responds to light in the same manner, as does the hen. Increasing day length causes release of hormones from the pituitary. These in turn cause enlargement of the testes, androgen secretion, semen production and stimulate mating behavior. Males used by breeders need to be lighted properly for maximum fertility and should not be lighted to stimulate gonad development until they will be used. The male should be lighted two weeks prior to the females for best fertility of the first eggs.