IACUC Learning Module - Poultry

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SPECIES INFORMATION-CHICKENS and TURKEYS

An intact adult male is called a "rooster," (under a year of age the term "cockerel" may be used); a castrated male is a "capon"; an adult female is called a "hen," under a year of age the term "pullet" may be used; a newly hatched bird is a "chick"; and a juvenile of either sex is called a "poult."

The White Leghorn, or crosses resembling this breed, are most commonly used for research purposes. These birds are white and quite large as adults (1.5-3 kg), with a single prominent pinkish-red comb (sometimes the day old chicks have the comb shortened or "dubbed" so that, as an adult, it is less likely to be injured). The White leghorn is an excellent egg layer of chalk white eggs.

The wild turkey, Meleagris gallopava, is a native of North America. It was introduced into Europe in the 16th century and is the ancestor of modern farmyard breeds. The turkey is large and has a bare, wattled head and neck.

The chicken has a small cerebral cortex with a large, well-developed hypothalamus. The optic lobes are well developed, suggesting that vision is important. Chickens can distinguish colors.

Respiratory System of the Chicken

One adaptation to flight is the development of pneumatic bones.  Instead of being filled with marrow, pneumatic bones are hollow and act as extensions of the respiratory system, which also includes the lungs, the tubes or bronchi leading to the lungs and the air sacs.  The lungs are rather rigid, attached to the ribs in the upper portion of the thorax, and do not expand or contract very much during breathing. There are four pairs of air sacs which reach from the neck to the abdomen and open into the pneumatic bones. The air sacs are delicate, thin walled and collapse when the chest is opened, so they may be difficult to see.

The skeleton is compact, lightweight and quite strong. Many of the vertebrae are fused, which provides sufficient strength to support wings for flight. The major flight muscles, the pectorals, are much larger in birds, and therefore their bony attachment, the sternum or breast bone, is also larger and stronger. In fact, the sternum is so large that it forms much of the bird’s ventral body wall. When you run your fingers along the ventral midline of the chest, you can feel the prominent ridge of the sternum. The sternum of birds may be called the "keel" bone, because it resembles the keel of a ship.
 

Diagram showing movement of sternum and ribs during respiration: A. Inspiration B. Expiration C. Sternum (keel)

It is primarily the change in pressure within the air sacs which allows air to pass into and out of the lungs. This change in pressure is largely due to the sternum, or keel bone, moving inward and outward during respiration.

The heart rate of an adult White Leghorn chicken is about 350 beats per minute. The heart is four chambered, with two atria and two ventricles. Chicken blood has red cells which are oval, biconvex and remain nucleated in the circulation.

Birds have retained the renal portal system, a more "primitive" feature not found in mammals. Blood from the back portion of the body flows from the iliac veins to the kidneys, where a valve allows blood to either pass on to the kidneys where nitrogenous wastes are removed, or return directly to the heart via the renal veins. Because of this renal portal system, drugs injected into the leg muscles may be toxic to the kidneys; usually it is better to inject into the large muscles of the chest.

The kidneys are large, long organs located tightly against the body wall associated with the backbone. Each kidney is divided into three distinct lobes. Urine passes from the kidney, through the ureters, which then empty into the cloaca.

The cloaca is a chamber common to the digestive, urinary and reproductive passages and opens externally through the vent.

Chicken urine consists of yellowish fluid with a white pasty substance largely made of uric acid. Uric acid is the main product of nitrogen metabolism in birds and is not water soluble; this is why solids make up part of the urine.

 

Male Reproductive Organs & Urinary Tract

The male possesses two testes, along the back, near the anterior ends of the kidneys. They are elliptical shaped and light yellow in color. Each ductus deferens opens into a small bump, or papilla, which is on the dorsal wall of the cloaca. The papilla serve as the copulatory organ. The incorrectly named, "rudimentary copulatory organ" is located on the medial ventral portion of the cloaca and is used to classify the sex of baby chicks.

The digestive system is somewhat different from mammals.
	The mouth lacks teeth and lips. Instead, the horny beak serves to bite off food. Barbs on the tongue help food to be moved backwards, so it can be easily swallowed. The esophagus forms a pouch, called a crop, where food is stored for brief time periods. From the crop, food moves down into the true stomach, or proventriculus, where hydrochloric acid and pepsin starts the process of digestion. Next, food moves into the gizzard, which is oval shaped and thick walled with powerful muscles. The chief function of the gizzard is to grind or crush food particles - a process which is aided by the bird swallowing small amounts of fine gravel or grit. It is written that the muscles of a turkey’s gizzard can crush a hickory nut, which requires 75 kg mechanical pressure!
From the gizzard, food moves into the duodenum. The small intestine is similar to mammals, there are two blind pouches or ceca, about 4-6 inches in length at the junction of the small and large intestine. The large intestine is short, consisting mostly of the rectum about 3-4 inches in length. The rectum empties into the cloaca and feces are excreted through the vent.

Reproductive organs of the female bird

Although bird embryos possess two ovaries and oviducts, only the left one normally develops and becomes functional with age. The ovaries appear like a bunch of grapes and in an adult will contain five to six developing egg yolks. The oviduct is usually along the left side of the abdomen and is divided into five regions: funnel or infundibulum, magnum where albumen is secreted, isthmus which secretes the shell membranes, uterus or shell gland, and the vagina which connects to the cloaca. Chicken eggs are incubated about 21 days before hatching. Turkey eggs are incubated for 27 days.

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