Avian Immune System – The Police of The Chicken Body

Like all animals, chickens, as well as other poultry, have immune systems like mammals do. Below is an insight to the defence of the avian body!

Primary Defences

Innate Immunity

Acquired Immunity

  • Passive Immunity
  • Active Immunity
    1. Cellular Immunity
    2. Non Cellular (Humoral) Immunity

    Skin: The skin is the first, and primary defence. It forms a physical barrier which blocks harmful micro-organisms from entering. Therefore, invasion can only occur if the skin is broken.

    Mucous Membranes: As the name suggests, these are membranes, covered in mucous! They are found lining the digestive tract, respiratory tract and several other body systems. The mucous carries the micro-organisms away, and expels them, via nasal discharge, or out the other side in the faeces.

    Immune System: Finally, if the invaders have bypassed all the other defences, the immune system comes in. It consists of various organelles and cells which are primed to target anything alien. Many of these are harmless, but the ones that cause disease must be eradicated!

    The immune systems primary role is to recognise foreign bodies and neutralize or eliminate them. This is done by lysis (rupture) and agglugation (clumping together) of foreign bodies, or phagocytosis (engulfing and de-activating).

    Innate Immunity is one of natures tools. It is the natural, or inherited ability to resist infection or disease.

    • Some birds are naturally resistant to diseases like lymphoid leukosis because they lack the receptors that the lymphoid leukosis virus infects.
    • Chickens have a high body temperature, so diseases from other animals are usually not a problem, because the pathogen is killed at high temperatures.
    • Normally, the skin and digestive tract are riddled with naturally beneficial bacteria. These stop invaders from gaining a foothold
    • The respiratory tract has fine hairs, called cilia. These are washed over with mucous and any bacteria foolish enough to dare penetrate the tract will be washed away and expelled out of the nose.

    Acquired Immunity is a very effective type of immunity that the bird gains over its lifetime. White blood cells or leucocytes are found in the blood. These are the ”police” of the body, and they hunt the criminals! There are phagocytes, which phagocytose (engulf and deactivate) intruders, and lymphocytes which release antibodies (special globulin proteins) to bind to and inactivate the antigens.

    There are two main ways in which acquired immunity works…


    1. Passive Immunity – This involves immunity transferred from individual to individual, for example, from hen to chick through the egg. In mammals, a similar process takes place through colostrum (antibody rich ”first milk”).

    3. Active Immunity refers to the immunity gained from acquiring a disease then defeating it. The  chicken keeps memory cells in the blood, so if the chicken is re-infected, antibody producion will occur so fast that the disease will not have time to cause symptoms.

    Passive immunity

    The first few days after hatching, a chick’s immune sytem is not functional, so it cannot fight invasion for itself. The solution to the problem comes through the egg. The mother passes on some antibodies which, although short lived, will guidde the chick through the first few days of life. These antibodies are from the mother’s acquired immunity, either from  vaccines or infection, then defeat of a disease.

    The level of immunity that is passed into the egg is similar to her own level, but after the 3 weeks of incubation, this drops to half. Therefore , it is valuable for the flock manager to keep the mother’s immunity levels high, to promote the health of her chicks. If vaccination of the chick is to be considered, remember that doing so too early could cause a subdued immune response, due to maternal antibodies attacking the vaccine, but if left too late, the chick will be open to disease, and may have an excessively high immune response.

    Active Immunity

    As I said above, active immunity is where the body fights off a disease, and keeps memory cells in the blood, so at the firt sign of re-infection,  antibodies are produced, and the disease cannot take a hold. This defence is effective, but only for specific antigens.

    Active immunity is divded into two parts, namely non-cellular (humoral) and cellular…


    Non-Cellular (Humoral) Immunity

    Non cellular (humoral) immunity involves antibodies, and the cells that produce them. Antibodies only exist for a short time, and are specific to their antigen. For example, the antibody for Infectious coryza, affects only the pathogen for Infectious coryza, and not the Infectious Bronchitis virus.

    When a pathogen enters the body, it is engulfed by a phagocytic WBC, known as a macrophage. It is then transported to and exposed to the B-lymphocytes (also known as B-cells).

    B-cells are produced (in the chick) by yolk sacs, the liver and the bone marrow. After 15 days of incubation, through to ten weeks of age, these cellsare moved to an organ known as the Bursa of Fabricius (BF). When required, the BF ”programs” the B-cells to attack the antigen with antibodies. The programmed B-cells then progress onto the spleen, the blood, the cecal tonsils, the bone marrow, the Harderian gland (in the eye) and thymus (an organ which ”educates” T-lymphocytes (T cells)).

    Destruction of the BF in chicks of a young age, due to Marek’s disease or Gumboro disease, means that the chick can never program B-cells, so cannot respond to most invasions, or vaccinations.

    When invasion occurs, the B-Cells release antibodies to fight the intruders. Macrophages also join the fight, coming to gobble-up the antigens which the antibodies have inhibited. After a war is over, the B-cells produce ”memory cells” which ”remember” the intruder, so should the intruder attack again, they can produce large amounts of antibodies, to generate a quicker and more effective response than the initial attack.

    Antibodies do not have the capability to kill disease directly, rather, they bind to the pathogens and inhibit their receptors. This means that they cannot locate, and bind to the target receptor.They also acts as a ”flag” for the phagocytes (macrophages) to detect invaders! Finally, though, it is up to the macrophages to engulf, and destroy pathogens.

    Cellular Immunity

    The cellular component of the immune response involves all cells that react to a specific antigen, except for those involved in antibody production (B-cells etc). The main players here are the T-lymphocytes (T-cells). These begin as the same stem cells as B-cells, but are programmed in the thymus rather than the BF.

    T-cells are produced and programmed to perform various functions, some T-cells assist B-cells and macrophages, these are known as helper T-cells, some produce lymphokines, others (directly) destroy invading organisms. Others still are known as suppressors, and inhibit the effects of macrophages and B-cells.

    This response was first discovered when it was found that birds with a damaged BF can still fight many infections and diseases!


    These are chemicals in the form of soluble proteins, that assist in activating other components of the immune response. Almost 100 different types have been identified!

    They work by:

    • Binding to WBC and increasing their ability to fight off invasion
    • Breaking down damaged, and invading cells
    • Increasing lymphocyte production
    • Performing many other related functions.



    Avian Endocrine Systems – Hormones in Poultry

    The Endocrine system consists of various glands and nodes which secrete hormones. Hormones are chemical messengers which travel in the blood to activate target cells. These target cells have special receptors, into which only certain hormones can fit. For example, testosterone act on the male gonads, but not the adrenal glands.

    Hormones tell the body what to do. The endocrine system is closely linked to the nervous system, because both deal with communications and co-ordination, but there are a few distinct differences.

    Hormones Act slowly, and for a long period of time. They cause gradual changes.

    Nerve Impulses Act very quickly, and only last for an extremely short period of time. The changes they cause are instant.

    Below are some of the main avian endocrine glands:

    Pituitary: The pituitary Gland is sometimes called the master gland. It sits in the brain base, and releases various hormones which trigger other endocrine glands to release hormones. It has two parts, the anterior and posterior lobe. It releases:

    • Natural Growth Hormone
    • Thyroid Stimulating Hormone
    • Adrenocorticotrophic Hormone (ACTH) – Stimulates the adrenal cortex
    • Sex hormones (LuteinisingHormone (LH) and Follicle Stimulating Hormone (FSH)) – To stimulate the sex glands
    • Melanin Stimulating Hormone – Unknown function (in birds)

    The posterior pituitary also produces arginine vasotocin and stores oxytocin both of which play a role in egg yolk release.


    The hypothalamus is located centrally in the brain, at the base. It produces oxytocin as mentioned above, and plays a role in controlling the anterior pituitary gland.

    Pineal Body: This is a small gland in the centre of the brain. It produces melatnin through the ue of tryptophan (a type of amino acid). Melatonin affects electrical goings-on in the brain, and behaviour, as well as sleep.The Pineal body has been described as a ‘biological clock’ and part of it function is to alert the hypothalamus as to when  to release certain hormones. An example of this is laying. In the wild, birds only lay in spring, because the pineal body ‘tells’ the hypothalamus that spring has come, and the hypothalamus begins producing LH and FSH.

    Adrenal Glands: These are a pair of small glands, some 9mm long, located in front of the kidneys. They have two regions, the adrenal cortex and the adrenal medulla. The cortex produces 3 hormones…

    • 8-hydroxycorticosterone – A hormone with an unknown function
    • Corticosterone – Stress reaction, protein breakdown, fat and carbohydrate metabolism
    • Aldosterone – Regulates sodium retention

    The medulla produces two compounds:

    Epinephrine – This plays a role in controlling blood pressure

    Norepinephrine – Fat metabolism

    Thyroid Glands

    These two glands are found at the base of the neck, each one lying at a different side.  They produce:

    • Triiodothyronine – Involved in feather (and beak and skin) development. Scientists think it may be involved in the moulting process
    • Thyroxine Regulates carbohydrate metabolism, heat production and promotes high blood sugar and growth

    Parathyroid Glands: are two assisting bodies located behind the thyroid glands. They produce Parathormone which regulates and controls the calcium level in the blood.

    Ultimobranchial bodies: These are located behind the parathyroid glands. They produce calcitonin and lower the blood calcium, thus calcitonin and Parathormone must be in balance.

    Islets of Langerhans: This group of specialized cells is located in the  pancreas. It produces two hormones:

    • Glucagon – Raises blood sugar, and affects fatty acids
    • Insuli – Lowers blood sugar


    Gonads or reproductive organs produces these hormones:

    • Testosterone
    • Progesterone
    • Oestrogen

    All of the hormones are needed in both genders, but the amounts vary. Hens need a lot more of the latter two, while cockerels produce much more of the former. When a cockerel is casrated, he becomes a capon and stops producing testosterone. Overtime, he takes on the behaviour, and to some degree, the appearance of a hen!



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    Mycoplasma – The Chronic Recurring Disease – Chronic Respiratory Disease (CRD)


    Mycoplasma refers to a family (also known as a genus) of bacteria that lack a cell wall. This means that common antibiotics such as penicillin, or other cell wall synthesis (the combination of several entities to form something different (such as the process by which amino acids form proteins, or proteins form an organelle)) targeting antibiotics (also known as beta-lactam antibiotics). They can be parasitic (living off other organisms) or saprotrophic (living off dead or decomposing matter).

    Mycoplasma in Chickens

    The most common type of mycoplasma affecting chickens is mycoplasma gallisepticum. This type of mycoplasma is parasitic, and affects chickens, wild birds, turkeys, pigeons and other fowl. It is the causative agent of chronic respiratory disease (CRD) in chickens and infectious sinusitis in game birds, turkeys, pigeons etcetera. It is transmitted either through the eggs of carrier hens, or by chicken to chicken (airborne) transmission. It is highly contagious and is spread rapidly when the birds sneeze.

    Some breeders breed without the knowledge that their flock is infected, therefore passing the disease on. Stress is thought to lower the resistance to the mycoplasma bacteria, and the disease sets in and the birds begin to exhibit symptoms. Some people dismiss this as the ‘common cold’, or think its ‘nothing’ and the disease is allowed to run riot throughout the stock.


    • Sniffling
    • Sneezing
    • Rasping or rattling in the throat
    • Foamy eyes and nose
    • Yawning

    More advanced symptoms include:

    • Loud, sharp ”Coughing” noise
    • Stiffness
    • Stretching legs and wings, sometimes trailing them
    • Difficulty balancing, sometimes even falling over


    Diagnosis is generally based on symptoms, and a blood test at the vets will give definite results. A course of medication will follow. Tylan is recommended for this purpose, but it is only available on prescription.

    Some people recommend Tylan injections rather than tylan oral, as this is faster and usually more efficient.


    A  vaccination is now available. The F-Strain is a low pathogenicity strain which gives immunity to the  birds for the laying season, but leaves them as carriers. It is, however, fully virulent for turkeys. Recently, 6/85 and ts-11 were introduced. These two live nonpathogenic strains give immunity, without making the inoculated bird a carrier.

    Can You Breed From Birds With Mycoplasma?

    Can You breed from chickens with Mycoplasma? Please comment below on how you feel about breeding from chickens with this chronic illness.

    Well, the long and short of it is that there is no easy answer. If you have birds with mycoplasma, and you want to breed from them, every situation must be treated as a different case!

    It all depends on how, where, when and why the birds have been infected, as well as the intensity of the infection.

    Also, some strains are more virulent than others, so this will also have some effect on the decision to breed or not to do so. It should also be taken into account, that once the birds are heavily infected, there are two ways of transmission. One of these occurs when the birds are stressed, and actively ”shedding” pathogens. This is when the disease is carried from bird to bird through the air. The other is when the bird is not exhibiting symptoms, but still carrying the disease. This is when the bird transits the disease through the egg!

    Birds which have been exposed to the disease, but have not contracted any signs are the obvious ones to breed from, if any. That said, they may still be carriers, but that could (theoretically at least) actually make the chicks immune to the disease! Because, as I discussed in my article on the chicken’s immune system (not yet published at the time of going to press), if an adult bird has immunity to a disease, some antibodies are actually passed on to the chick! But, it is a double edged sword, because, at the same time, disease pathogens could have been passed on, and this leaves the chick open to disease.

    Birds that have been treated for mycoplasma have obviously had the disease more severely, so chances are, the oviducts would have been infected, guaranteeing the chicks to come down with the disease, UNLESS you medicate the birds with tylan, or similar, and collect the eggs that you will use for hatching  during this period of medication. IF you are lucky, the tylan may have intercepted pathogen transmission to the egg, or in some mysterious way, avoided infection!

    Obviously, placing eggs under an infected hen is NOT advised, because she will only infect them, even if the eggs were uninfected! Therefore, an incubator is a better answer. An uninfected hen is not advisable either, unless she is vaccinated with a non-pathogenic strain, because if the eggs were NOT pathogen free, they will infect the previously uninfected hen!

    So, can you breed from chickens with Mycoplasma? Yes. Yes you can, BUT you need to look at EVERY SINGLE CASE seperately, and evaluate  the risks and benefits, because, at the end of the day, it’s not really worth taking the risks of breeding from infected birds, unless you are trying to rescue a breed on the edge of extinction!!!


    Avian Skeletal System – The Bones of The Bird

    All animals have skeletons of some type, be it an endoskeleton, exoskeleton or a completely unique one!!!! While chickens skeletons may look akin to all the rest, their are subtle differences. Their skeletons are built like birds skeletons, modified for flying (even though modern chickens dont fly!). So how is the avian skeleton different?

    The tail consists mostly of feathers. In fact, its only bone is a few very small bones, fused together to form the pygostyle. The head has also been made smaller than in other animals, to allow for good balance while flying. Chickens sternums are also flat, yet light to provide anchorage for the main flight muscles. The ribcage has a structure called the uncinate process. This is seen as flaps which overlay the ribs and attach one rib to its neighbour. This provides support and extra strength to the ribcage and ensures that it does not collapse during flight.

    The entire body is very rigid. The spinal processes are fused to help with flight, the ribs are fused etcetera, so acces to food is hard. For this reason, the neck is long! It also help to protect the bird from jarring the brain as it lands.

    The skull, sternum and some of the vertebrae are pneumatic bones. This means that they are part of the respiratory system, in fact, they are hollow and contain air sacs. Another type of modified avian bone is medullary bones. These are those such as the tibia, ulna, toes, pubic bone and others, and provide an important source of calcium which is used when the hen is laying. In fact, a hen uses 47% of her calcium store to create an eggshell. Commercial laying hens cannot get enough calcium from diet alone, and rely on this vital store to avoid thin, or non existent egg shells.


    Chicken bones are similar, yet different. The tail is fused, yet articulating, the neck is also movable, but the remaining vertebrae are fused. Some bones, especially the sternum, are large and flat to provide a hold for flight muscles.

    There are two main types of bone. The pneumatic bones have air sacs in them to help flight, and act as a part of the respiratory system. Medullary bones provide an extra, and essential calcium store.

    The function and science of the avian ear

    Do Chickens have ears? Yes! And in this article I will explain how they work.

    Even though chickens ears are seen only as small,  fleshy red or white earlobes, or auriculars (also known as ear coverts), the inner ear channels and amplifies sound, and plays a significant role a one of the senses.

    Near the auriculars and below and behind the eye, the ear is located. The auriculars channel sound waves into the ear opening,  and towards the eardrum, a thin membrane that vibrates in accordance with the sound waves. The waves are passed down the columella, one of the smallest bones in the avian body, and transmitted to another membrane called the oval window via the cochlea in the middle ear. The cochlea is filled with fluid, and tiny hairs called cilia are attached to its walls. They move with the sound vibrations, as blades of grass do in the wind. Vibrations are translated into electrical impules, and sent to the brain via the auditory nerve.

    When human cilia are damaged, they never re-grow, and so throughout life, hearing slowly decreases. The same happens in birds, right? WRONG!!! Birds can regenerate their cilia!!!

    Avians also have semicircular canals, the saccule and utricle, which regulate balance, just as they do in humans.

    I hope this was interesting, feel free to browse my website!


    Eni’s Rare Breed Chickens has Twin Websites!!

    Enis rare breed chickens has a twin website!!!! It is called TX Stock Photos. It sells photos, graphics and videos, and has a wide range of subjects, but specializes in quality countryside and equine photos. You can visit it here. It has not yet launched, but will do so in 2013.

    It also has a blog, where regular information on photography, new camera releases and tutorials in using adobe photoshop is posted. The blog is a rich yet reliable information fest for photographers of all abilities! You can visit the blog here.

    Check out its facebook page and like it! Follow on twitter and Google +!

    It is also twinned with Pony Galaxy,  a website that is… All about horses and ponies!!! This site will make all horse and pony lovers feel at home. In paradise in fact! This blog is full of reliably sourced information, and is really worth checking out! Also check out its facebook pagetwitter page and Google + page.

    Banish Bad Behaviour!! How-to Have Harmonious Hens!!!

    Banish Bad Behaviour!!

    In general, chickens are social animals, living in peace and harmony. When a new bird is introduced, this harmony is temporarily disturbed as the hens squabble to sort out their pecking order. The pecking order is the heirachy by which chickens live. The hens have a little squabble, and the hen that wins is the dominant hen. She gets access to the food and water first, and can put any hen who dares confront her back in her place with a sharp peck. On the other hand, the lowest ranking hen gets to go to the food last, and can be pecked at by any hen. Because of this system, hens live in peace, but when the balance is upset, peaceful Poppy can turn into ferocious Frostie.

    In this article, I will cover a few points of bad behaviour and give some tips on how to deal with it.


    Excess noise

    It is usually the cockerel who makes the most noise, while crowing, this can only be avoided by not keeping a cockerel. Cantrary to popular belief, it is not necessary to keep a cockerel to get eggs. The cockerel is only needed to fertilize eggs. Sometimes, a hen will make lots of noise, when she has layed an egg. If this is her habitual egg laying noise, it is not possible to stop her from making the noise, but a few steps can be taken to reduce the amount of noise she makes. These include:

    • Reduce boredom (see below)
    • Reduce stress
    • Practise good husbandry



    Overcrowding and small pens can cause boredom, which often manifests itself as feather pecking in adults and foot pecking in chicks. Chickens are attracted to red, (which is why feeder bases are often red), so if blood is drawn cannibalism can be the result. You should always keep some genitian violet spray handy because this is antibiotic, and stains the wound purple, to stop the chickens from attacking the hen.

    Boredom can be prevented or alleviated by;

    • Scattering grain over the ground to encourage them to forage ‘naturally’
    • Hanging up bunches of green leaves for them to peck at
    • purchasing, and hanging up blocks of seed



    This often happens when two cockerels come in contact with each other. This is why cockerels should be kept apart. This takes place over hens, territory, etc.

    Fighting can also be found with hens, when a new hen is introduced, for example. This is done to establish the pecking order. Once this is established and all the hens know where they stand, peace will return.

    Egg eating is addressed here. Corresponding section highlighted pink.

    Function and Utilization of Essential Vitamins and Minerals in Chickens

    Just like for us humans, to chickens, vitamins and minerals are very important for health. Lack of  of these, known as a deficiency,  causes problems, varying from something more minor such as decreased egg production to much more serious conditions, such as anaemia and death.

    Chickens need all known vitamins and minerals, with the exception of Vitamin C.

    Below is a list of Vitamins and Minerals, and the effects suffered by chickens in case of deficiency.



    Vitamin/ Mineral

    Vitamin and Mineral Function Deficiency symptoms

    Vitamin A (Retinol)

    Good feathering, egg production, reproduction Weakness, lack of growth, decreased egg production
    Thiamine (B1) involved in enzyme systems, Loss of apetite, Death, chick paralysis
    Riboflavin (B2) Essential in many enzyme systems Poor growth, poor egg production and curly toe
    Pantothenic Acid Essential for Growth, hatchability, feathering Dermatitis and lesions on feet and around beak and eyes
    Niacin Fat protein and carbohydrate metabolism Bowed legs, inflamed mouth cavity
    Choline Fat metabolism, Fatty liver, poor growth
    Vitamin B12 Growth, good hatchability Anaemia, poor growth, embryonic mortality.ss
    Vitamin D Bone growth, egg shell production, Calcium and Phosphorus utilization Rickets
    Vitamin E Normal reproduction and fertility. Antioxidant Enlarged hocks, crazy chick disease
    Vitamin K Blood clotting, haemorrhage
    Folic Acid Prevents perosis, good feathering Anaemia, poor feathering, poor growth, anaemia
    Biotin maintains blood glucose levels, involved in carbohydrate conversion Perosis, poor hatchability
    Below are some important minerals essential to chickens’ health
    Calcium Important for healthy bones, and strong eggshells, and hatchability Soft shelled eggs, poor hatchability and rickets
    Cobalt Activates enzymes, synthesises B12, needed for pyrimidine synthesis Slow growth, mortality, reduced hatchability
    Copper Iron metabolism, controls the movement of iron anaemia
    Iodine Thyroxyn synthesis, regulates neuromuscular functions goitre
    Iron Important in haemoglobin formation, Transports oxygen anaemia
    Magnesium energy metabolism, nerve impulse transmission Sudden death,
    Manganese Important in the formation of bone cartilage Perosis, poor hatchability, bone shortening, bowing bones
    molybdenum Synthesis of haemoglobin Deficiency rare, excess more common, causes reduction in copper availability
    Phosphorus Component of bone, helps bone structuring Poor egg shell quality, rickets, bad hatchability
    sodium Acid-base balance, salt balance dehydration
    Selenium Antioxidant, increases vit. E absorbsion, Poor fertility and hatchability
    Zinc Essential for over 2oo enzyme systems Short bones, poor feathering, poor eggshell formation



    Chickens respiratory system- science of breathing and lungs

    Because of the energy required for flying,birds have a very high demand for oxygen. Even though chickens don’t fly much, they still maintain these characteristics.

    han being a single ‘bag’ for air, they have air sacs spread around their organs, and in their bones which help keep the pressure of air in the lungs constant.

    When a bird inhales, half the air passes through bronchi to the posterior (back) air sacs, and the other half goes to the anterior (front) sacs and the lungs. That in the posterior sacs is emptied into the lungs, rather than alveoli, gas exchange takes place between the blood capillaries and the air ‘capillaries’ known as para bronchi. Compared to mammalian gas exchange, that that takes place in birds is much more efficient because the partial pressure is the same as that of the environment.

    Their lungs are quite different to mammal lungs, because, rather t


    They have no diaphragm, and therefore air flows into the lungs and is pushed out by muscular contraction.

    Located at the bottom of the trachea (windpipe) is the syrinx, the birds voice box, and as they exhale they can crow, cluck etc…

    Hope you liked this post, please check ot my other posts!