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The Organs of a Chicken’s Immune System

You need to understand the chicken immune system, to familiarize you with that defense network, because flock owners need to know how to help their chickens protect themselves against and deal with infectious diseases. A bird has built-in defenses against invading disease-causing organisms, such as bacteria or viruses.

[Credit: Illustration by Kathryn Born]
Credit: Illustration by Kathryn Born

The following list walks you through these different parts of a chicken’s immune system:

  • General: Some of the immune defenses are general, which means that they guard against a wide range of organisms, rather than a specific one. Unbroken skin is the frontline of the general defense network against disease. The microbes that normally live on the skin and in the gut also defend against invasion attempts by foreign organisms.

    The lining of a chicken’s windpipe, like that of other animals, is covered with mucous and waving hairs, called cilia, that collect and sweep inhaled dust and other gunk (like bacteria) up and away from the lungs.

    Maybe the sweltering body temperature of chickens, which fluctuates a couple of degrees around 106 degrees Fahrenheit (41 degrees Celsius) in healthy chickens, discourages some types of disease-causing organisms from setting up shop. Also, genes play a role in protecting some strains of chickens against some illnesses.

  • Antibodies: Like humans and other animals, chickens make antibodies, which are very specific defense molecules programmed against particular organisms. For example, antibodies for infectious bronchitis virus protect chickens only against infectious bronchitis virus, and not Newcastle disease virus.

    A chick can receive antibodies from a mother hen through the egg. These hen-donated antibodies last for the first couple of weeks of the chick’s life, protecting the chick until her immune system is up and running, producing antibodies of her own.

    In mammals, the spleen, tonsils, bone marrow, lymph nodes, and the thymus (a spongy thingy in the upper chest of young animals) are organs that have important roles in making antibodies and other molecules of the immune defense network.

    Birds have all that, too, except for the lymph nodes, and birds keep their tonsils in their ceca. Also, birds have a couple of other important outposts in the immune defense system: the bursa of Fabricius, which is a pouch above the cloaca of a young bird, and the Harderian glands, near each of the chicken’s eyeballs.

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