Integument
The skin of poultry is similar to mammalian skin in that it is an organ composed of an overlying stratified squamous epithelium and the underlying vascular dermis. Avian skin is typically very thin.
it lacks sweat glands entirely. Most of the skin is not particularly well vascularized, but in birds incubating eggs brooding patches may develop on the breast. In these areas, the skin thickens, becomes more vascular, and feathers are lost. The brooding patch provides the incubating eggs with intimate contact with the warm skin of the parent bird.The presence of feathers is the hallmark of class Aves. Like the hairs of mammals, feathers are keratinous in nature and grow from an epidermal follicle that encircles a dermal core.
The vascular feather pulp, an extension of dermal tissue into the shaft of the feather, is prominent only during growth. Trauma that breaks the shaft of a large growing feather (a so-called blood feather) may lead to considerable hemorrhage.
There are two main types of feathers seen in poultry: contour feathers, which comprise the flight feathers and those that cover the body, and the fluffy down feathers. Both types possess a semirigid shaft with multiple barbs arising from it forming the vane. Contour feathers are characterized by the orderly interlocking nature of the barbs, whereas down feathers lack this systematic linking of barbs.
Feathers are not uniformly distributed on the body of the bird, occurring instead in well- described feather tracts. some locations on the bird’s body are relatively free from contour feathers. These are the apteria (singular apterium), which in domestic fowl are especially notable under the wings. Feathers are replaced in most birds once or twice a year, and in most species the molt proceeds in a sequential way so as not to render the bird flightless due to insufficient flight feathers.
Ducks and geese (Anseriformes), however, are unable to fly for several weeks during their molt.Chickens of breeds selected for high egg production may molt after a typical 12-month laying period. However, some birds may molt during this laying period, and low-producing hens often stop egg production if they molt at this time. Restriction of food and water and decreasing periods of light will induce an entire flock to stop laying and begin molting (a forced molt). During a forced molt, the reproductive system regresses and circulating levels of prolactin, luteinizing hormone (LH), estrogen, and progesterone decrease. After a forced molt, and after photoperiods and diets are corrected, hens typically enter a new laying period with improved egg production. The use of forced molts as a management tool has become controversial in part due to the restriction of food and water required to induce the molt.
Although avian skin is nearly glandless, domestic fowl have a large, well-developed sebaceous gland that opens dorsal to the caudal vertebrae. This bilobed gland, the uropygial gland, opens onto a raised papilla between the tail feathers. The oily secretion of the uropygial gland is distributed over the feathers by the preening behavior of the bird. It is especially large in water fowl, in which it has the critical function of waterproofing the feathers.
The feet and legs (shanks) of most domestic fowl are covered with scales that are thickened epidermal patches. A few varieties of chickens have been bred with feathered legs (e.g., the Brahma). The spur of male chickens and turkeys (gallinaceous birds) is used as a weapon in fighting. It has a bony center and is surrounded with epidermis, but it is not considered a “toe.” The three forward-facing digits (numbers two through four) are joined by webs that are largest and most obvious in the Anseriformes.
The face of gallinaceous birds is decorated variously by modifications of the skin that probably function at least in part in sexual display.
The comb is placed on the dorsal midline and exhibits considerable variation in appearance among different breeds. Paired wattles hang from the ventral face, and the ear lobes decorate the side of the head near the external ear. The heads of turkeys are essentially featherless and covered with irregular bumps called caruncles. In addition to the comb and wattles, turkeys have a fingerlike snood that hangs from the dorsal aspect of the face down across the beak.The yellowish color of the skin and associated structures of most domestic chickens is due to an accumulation of a carotenoid pigment, xanthophyll, which is derived from dietary items such as corn. This pigment also contributes to the yellow color of an egg yolk, and when a hen begins laying, the yellowish color of the skin and associated structures is lost as pigment is deposited in the eggs. Color is lost in sequence from the skin around the vent (anus), eye ring, beak, and shanks, thus a hen with pale shanks has been laying for some time. Turkeys cannot accumulate carotenoid pigments in the skin and hence have a white skin.