New episode of the podcast is up! Find it on Podbean, or wherever you get your podcasts.
Homestead News:
I did adopt that rooster from animal control and he is gorgeous!! He's taking such great care of the hens, and I love finally being able to let them roam. I've been spending a lot of time just sitting out with them and watching them explore.
Meatbutt's bumblefoot continues to be an issue. Although most of the swelling has gone down, the abscess came back and I spent a while digging and flushing it out. I might have finally got it all. Fingers crossed!
I've been non-stop raking leaves, mulching beds, and putting everything to bed in preparation for winter. I'm so tired but feeling accomplished!
Hive news:
-We've had such lovely weather that I put 2:1 (sugar/water) syrup out for all the hives. I nestled the feeder jars in the quilt boxes so I didn't have to dismantle my previous winter prep.
-I was able to condense one of the nucleus colonies down and add a quilt box so they're finally all squared away for winter.
-Visited a mentee's hive and finally got to inspect it. It hasn't been inspected in 3 years and was falling apart a little (the frames, mainly). What I saw lines up with what I've been seeing in my own apiary (dearth hit them hard but they're shoring back up the stores). Advised on feeding syrup during nice weather, putting on fondant for winter, and adding insulation. I also intend to help her re-queen the colony in the Spring because these bees are defensive and moderately aggressive. Not a fun hive to work! She needs a gentle colony to help her enjoy the hobby.
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Episode 32: Chicken Biology, Part 1
Sources:
‘The Chicken Health Handbook’, Gail Damerow (primary)
‘Raising Chickens for Dummies’, Kimberley Willis, Robert T. Ludlow
Immune System
Function: defend the body against disease-causing microorganisms and pathogens
3 primary lines of defense:
Feathers, skin, and mucous membranes; hinder entrance of pathogens into the body
Cells and chemicals; circulated in the bloodstream
Enhanced immunity; aka immunological memory, the initial immune response establishes increased future response
Protective Feathers
6-8% of a chicken's weight is made up of their feathers
Protects the skin from injury and sunburn, conserves body heat, and provides some degree of waterproofing
Chickens lose and replace feathers (moult) yearly, which happens over weeks (approximately 14-16 weeks) so the bird is never completely featherless, and occurs in late summer through fall
Feathers grow from follicles arranged in 10 symmetrical tracts located on the head, neck, shoulders, wings, breast, back, abdomen, rump, thighs, and legs
The follicles are linked by tiny muscles that raise and lower the feathers as needed (such as puffing up in cold weather)
These feather tracts (called pterylae) are separated by featherless areas (apteria)
Apteria may contain some down
Down: feathers closest to the body that lack the barbs and strong central shaft that other feathers have, which is why they’re so fluffy!
These featherless areas help cool the chicken in the heat by exposing the skin to circulating air
Anatomy of Feathers
Feathers are made of keratin (same as our fingernails and hair)
Each has a hard, central shaft
Bottom of each mature shaft, which is hollow, is called a quill
Immature feathers (pinfeathers or blood feathers) have a vein in the shaft, and grow covered in a thin, papery coating that wears off or is groomed away
When immature feathers reach their full length, the vein in the shaft slowly dries up
On both sides of the shaft are rows of barbs, and on these barbs are rows of barbules
Barbules have tiny hooks along their edges that connect them to their neighbours, creating a smooth feather
When chickens groom/preen, they are smoothing the feather barbs to help them lock together
Chickens also have a preen gland; a pea-sized uropygeal gland that secretes oil to condition and waterproof feathers
The colour of feathers comes from pigments in feathers and from the way keratin is layered
Colours from pigments: black, browns, reds, blues greys, and yellow
From keratin layering: iridescence
Skin and Mucosa
The skin is the largest organ in the body, making up 8% of a chicken’s weight
Chicken skin is thinner and more delicate than a mammal’s
Colour varies on breed, diet, age, egg production rate, and health; for instance, a young chicken with very little fat might have skin that is blue-ish in colour
Colour of the feathers does not effect the colour of the skin
Most breeds have yellow of white skin but some have all black (like Silkies)
On the skin, live beneficial microbes that keep harmful ones away via a process called ‘competitive exclusion’
Competitive exclusion: 2 species competing for the same limited resources cannot coexist at constant population values (one ultimately fails)
If the skin is damaged then these beneficial microbes can enter the body and cause disease
Mucosa (aka mucous membranes) line the openings of the body and also contain beneficial microorganisms or microflora, which also use competitive exclusion
These microbes are assisted in their defense role by moving fluids (mucous and tears; flushing action) and enzymes that combat invading microorganisms
Lymphatic System
Uninjured skin and mucosa are a strong defense against pathogens but certain factors (nutritional deficiency, disease, and injury) can allow pathogens to penetrate the body, which is when the lymphatic system comes into play
Lymph: watery fluid derived from the blood that accumulates in spaces between the body’s tissue cells
All body fluids lubricated by lymph
Lymph also contains lymphocytes; specialized white blood cells that neutralize or destroy invading microbes
Lymphocytes recognise invaders as antigens, which are any protein that differs from those naturally occurring within the body
When an antigen is detected, lymphocytes produce antibodies or immunoglobulins, which attach to the antigen and break down their defenses
Humans have a system of organized lymph nodes but chickens do not
Instead, chickens have lymphoid organs
Lymphoid: any body tissue that produces lymphocytes and antibodies
Lymphoid tissue occurs primarily in the spleen, thymus, and cloacal bursa but is also found in bone marrow, the intestines, respiratory system, and head
Spleen
Dark red, round organ
Usually ¾ inch in diameter
Made up of red pulp and white pulp
Red pulp: destroys worn out/old red blood cells
White pulp: forms white blood cells/leukocytes
Both pulps produce antibodies
Not considered a vital organ; if it ceases to function, other organs can take over its job
Thymus
Made up of several paired, flattened, pale-pink lobes of irregular shape; strung along the jugular vein on both sides of the neck for almost the entire length of the neck
# of pairs: 5-8
The thymus shrinks with age
Thymus and cloacal bursa are the chicken’s primary lymphoid organs
Both produce functional immune cells that are collected and stored by secondary lymphoid organs
Small lymphocytes produced in the thymus are called T cells
T cells: defend on a cellular level (known as cell-mediated immunity)
B cells: lymphocytes produced in cloacal bursa that produce antibodies that defend body fluids (non-cellular/humoral immunity)
Both B and T cells begin as stem cells produced during incubation in embryo’s yolk sac, liver, and bone marrow
The circulatory system delivers these cells to the thymus and cloacal bursa where they mature into B and T cells
Cloacal Bursa
Pale, grape-shaped organ above the cloaca
Largely responsible for controlling immunity and activating antibody production in chicks
The inside of the cloacal bursa consists of 2 dozen parallel folds of about 10,000 follicles that provide an ideal environment for the development of antibodies
In young birds, the cloacal bursa takes in fluids (known as ‘cloacal drinking’); a form of inoculation against environmental pathogens
Reaches maximum size between 6-12 weeks of age and then begins to shrink
By the time the bird is sexually mature (at 4-5 months), it is no longer functional
Certain diseases and nutritional deficiencies can cause premature atrophy of the bursa, resulting in a permanently compromised immune system
GALT, BALT, HALT
GALT:
Gut-Associated Lymphoid Tissue
Clusters of lymphoid nodules along the digestive tract
Majority in parts of the small intestine (called Peyer’s patches), base of the ceca (cecal tonsils), and in the Meckel’s diverticulum
Function: to protect against intestinal diseases
Accumulates as chick matures; maximum acquired at 16 weeks
BALT:
Bronchial-Associated Lymphoid Tissue
Located in the trachea and bronchi
Function: protect against inhaled pathogens
Develops as chick grows; well developed by 8 weeks
HALT:
Head-Associated Lymphoid Tissue
Includes nasal glands, tear glands, mucous membranes of the eyes, and a relatively large Harderian gland behind each eyeball
Function: protects the eyes, nasal cavity, and upper airways
Memory Cells
When T cells and B cells are exposed to an antigen, they develop antibodies specific to target that antigen, as well as memory cells that store information about the antigen
If the antigen enters the body again, the memory cells produce antibodies that attack the antigen
Over time, the immune system develops a wide range of antigen-specific memory cells
Once various lymphoid organs atrophy (as previously discussed), antigen-specific memory cells becomes the primary immune response
If a chicken is exposed to pathogens not experienced in its youth, the immune system has no memory cells to combat it and therefore no immune defense
This is a big part of why quarantine is so important!
Muscular System
Muscles = meat!
Muscle: made up of bundles of fibrous tissue with the ability to contract
3 kinds of muscle:
Cardiac: controls movement of the heart
Smooth: controlled by autonomic (involuntary) nervous system
Skeletal: voluntary movement (also the kind we eat!)
Different fibers make some muscles dark (dark meat) and some light (white meat)
Dark: heavily used like thighs and legs
Light: breast and wings (less active)
Muscles alternate contracting and relaxing, using a system of levers created by the chicken’s joints and skeletal system
Bones have ridges and bumps where muscles attach
Skeletal System
Functions:
Provide framework for muscles (allowing movement)
To support the body
To protect internal organs
To store and release calcium
To in respiration
Medullary Bone
Some bones of the skeleton contain marrow and medullary bone; a fluctuating substance
Lies inside the structural bone as a lining and extending as many tiny needle-like projections into the marrow
Unique to female birds
Fun fact! Since it’s unique to females, it is one way that scientists sex dinosaur fossils
As the pullet reaches sexual maturity and estrogen is produced, roughly 2 weeks before she lays her first egg, her system switches from developing structural bone to packing some of them with medullary bone
From then on, as long as she continues to lay, specialized cells in her bones reabsorb medullary bone and, to some extent, structural bone to provide calcium for egg shells
Laying hens that produce an egg a day cannot absorb enough calcium from diet alone to create a sturdy egg shell
Instead, she uses a considerable amount of skeletal calcium, gradually losing structural bone
Osteoporosis: condition where the bones become fragile and fracture more easily
Genetics, environment, and nutrition all influence bone loss
A diet deficient in calcium leads to faster skeletal calcium depletion; results in laying fewer eggs and then eventually stops
An otherwise healthy hen that stops laying will reduce estrogen production and resume formation of structural bone, restoring strength to her skeletal structure
Not a fun fact: highly productive hens kept in cages (like how most laying hens are treated) can develop cage fatigue, a form of paralysis that results in death due to the inability to reach food and water. Cages with solid bottoms seem to reverse this, as does removing the hen from the cage for a few days. Another reason not to buy grocery store eggs!
Pneumatic Bones
Found in both sexes
Contains diverticula (blind tubes) extending from the air sacs
These bones are hollow, reducing birds weight for flight
They increase the flow of oxygen for metabolism
Also serve as a cooling system
Pneumatic: Latin ‘pneumaticus’, “belonging to the air”
Connect bones to the respiratory system
Fractured pneumatic bone can lead to difficulty breathing and lead to an air sac infection
Skeletal Issues
Leg weakness: common in large breeds
Keep young birds off slippery surfaces, feed a balanced diet, refrain from breeding birds with lameness or deformity
Lameness: not always skeletal in origin; can be neurological in nature, or due to muscle or nerve damage
Inflammation of the joints or synovial membrane
Synovial membrane: thin membranes lining joint cavities and tendon sheaths; secrete synovia, a fluid resembling thin egg whites that lubricates the joints
Synovitis: inflammation of the synovia membrane; causes excess synovia to be secreted, making the joint warm and swollen (painful). Often effects the hock (ankle joint).
Non-infectious and infectious synovitis
Bursitis: inflammation of the bursa; caused by pressure, friction, or injury of the membrane surrounding the joint
Bursa: small fluid filled sacs that cushion pressure points at joint
Keel (breastbone) bursitis is most common; known as ‘breast blister’; caused by pressure against the keel
Respiratory System
Includes: nasal cavity, sinuses, larynx, trachea (windpipe), syrinx (vocal organ), bronchi, lungs, and air sacs
Functions:
Circulates oxygen throughout the body
Removes carbon dioxide
Aids in thermoregulation
Allows chicken to vocalize
A chicken’s voice box is not like our own; it has no vocal chords, and instead consists of the syrinx at the bottom of the windpipe, where the trachea splits down into the two bronchi
The larynx in chickens functions purely to prevent food from entering the windpipe
Chicken vocalizations require cooperative effort of tracheal muscles, syrinx, air sacs, and respiratory muscles
Some muscles contract to force air from air sacs into the syrinx; others exert tension to alter the shape of the syrinx to create different sounds
The syrinx cannot be removed to prevent crowing in roosters due to its critical location (also this would be very cruel!)
Air Sacs
All birds have an extensive system of air sacs (thin-walled, bubble-like pockets) that circulate fresh air into various parts of the body
System extends around the internal organs, filling almost all the ‘empty’ cavity spaces, and into the pneumatic bones
Air sacs organized into 2 sets: one toward the front of the body (anterior/cranial air sacs), and one toward the rear (posterior/caudal air sacs)
Soon after a chick hatches, the anterior air sacs expand into the vertebrae of the neck
As the chick grows, the posterior air sacs expand into the vertebrae toward the pelvis
By maturity, air sacs have spread throughout the vertebrae
There are nine air sacs in total; all but one of which are paired
9 air sacs:
-Forward/anterior: 1x Cervical (neck, above esophogus); 2x Interclavicular (shoulder, between wishbones), 2x Thoracic, anterior (in front of lungs)
-Posterior/caudal: 2x Thoracic, posterior (behind lungs); 2x Abdominal (surrounding intestines)
Largest pair is the Abdominal
Air sacs fill and release air based on size of the body cavity, which is controlled by muscle movement
When resting, the abdominal muscles control breathing
When active, greater muscle movement causes body cavity to expand and contract, increasing air flow into air sacs
If a chicken still needs more oxygen, it flaps its wings to generate greater airflow; expanding air sacs further and drawing more air into the pneumatic bones
Fan fact: this is why roosters flap their wings before crowing! Big breath!
Air sacs are flexible but chicken lungs are rigid; they are solidly attached between the ribs and so unable to expand as our lungs do
Instead of lungs expanding and retracting, the air sacs do so instead
Incoming air goes directly from the trachea to the posterior air sacs then passes through the lungs into the anterior air sacs
Outgoing air goes directly from forward air sacs but passes through the lungs before going out of the rear sacs
Thus, air passes through the lungs in the same direction and the bird obtains oxygen on the in and out breath
This steady flow enables sufficient oxygen to maintain its high metabolism
Never squeeze your chickens!
Due to the expansion of the body cavity allowing airflow/breathing, squeezing tightly enough to prevent this is dangerous
This is especially an issue in baby chicks, who are very delicate
Always supervise young children when handling chicks, and be mindful yourself to never hold them too tightly
If a chicken seems to be struggling to breath, lift its wings or let it drop down a short distance to trigger reflexive flapping; this generate airflow (also works if the bird appears to have stopped breathing)
Respiratory Defenses
Trachea is lined with short, tiny, hair-like structures called cilia
Cilia vibrate/wave to whisk pathogens and dust particles back untoward the beak to keep them from the respiratory system
Excessive dust can overwhelm the cilia and cause them to become ineffective
The trachea produces mucus to help the cilia trap inhaled pathogens
Too much ammonia in a coop can cause thicker mucous production that inhibited the movement of the cilia
The lungs host scavenger cells that seek and destroy pathogens and dust before they spread to the air sacs
Mucous can also collect at the bottom of the trachea, clogging up the bronchi, which blocks the air from entering the lungs and air sacs, causing suffocation
Clean environment/coop is vitally important!
Airsacculitis
Inflammation of the air sacs
Caused by bacterial infection
Usually affects younger chickens, especially broilers
Signs including failure to eat, rapid weight loss, coughing, strained breathing, and high death rate amongst the flock
Air sacs have few blood vessels and most antimicrobials medicines are delivered through the bloodstream so this condition is hard to effectively treat
Ruptured Air Sacs
Can occur at any age
Rough handling, fighting, crash landing or falling can cause this
Considered a form of airsacculitis, ruptured air sacs allows air to leak into the chicken’s body, causing the skin to puff up and give the bird an inflated appearance
Also known as ‘windpuff’
Technical term: subcutaneous emphysema
Subcutaneous: under the skin
Often the rupture will heal on its own
Isolating the chicken might be needed to reduce stress and aid in healing
Deflation of the air pocket can be done with a sterile needle if it is causing an inability to move or pain; likely will need to be repeated, though
If the rupture is very bad, the chicken will likely die; this is seen more often in chicks
Respiratory Disease
The most common cause of death in chickens
Causes can be nutritional, parasitic, bacterial, fungus, viral, or environmental
Most serious ones are viral; spread easily in moist air, expelled by sick bird when coughing, sneezing, or just breathing
Respiratory distress is sometimes a reaction to vaccination, especially for Newcastle disease and infectious bronchitis
RI diseases often occur in combination so a flock cured of one disease might still show symptoms of a second
Best defense: develop flock’s genetic resistance via good breeding practices and providing a healthy, well ventilated living environment
Also, quarantine new additions!
Signs/symptoms include: laboured breathing, sniffling, gasping, coughing, sneezing, wheezing, runny nose, foamy/watery eyes
Vital Statistics
Average lifespan: 5-8 years
Maximum lifespan: 18-22 years
Max. productive life: 12-15 years
Body temperature (average):
Adult: 103F/39.4C
Adult, deep body: 107F/41.7C
Chick: 106.7F/41.5C
Respiration rate (at rest)
Cock: 12-21 breaths per minute
Hen: 31-37
Heart rate (average)
Adult, large breed: 250 beats per minute (BPM)
Adult, small breed: 350 BPM
Chick: 300 BPM
Important note: chicken heart rate and temperature are so variable that they’re not considered a reliable diagnostic tool
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Next episode, Chicken Biology Pt2, will cover the digestive system, male reproductive system, nervous system, and circulatory system.
Thanks so much for listening/reading! I hope you're all staying safe and healthy. Remember to hug your hens (and roosters!) and then wash your hands. And enjoy the Autumn weather and sights while you can! Chappie is embracing all the leafpiles.
