Stress & Its Impact on Chicken Health

“Everyone knows what stress is and no one knows what it is.” – Hans Selye

In 1915, American physiologist Walter Cannon introduced the concept of the fight-or-flight response, a physiological reaction to a perceived harmful event or threat to survival.

The sympathetic nervous system reacts to stressors by releasing the hormone cortisol, which increases blood pressure, blood sugar and suppresses the immune system to create a boost of energy. Think of it as pressing down on a gas pedal. When the threat passes, cortisol levels fall.

But if the brain continues to perceive something as dangerous, the body continues to stay on high alert. The parasympathetic nervous system – the brake – dampens the stress response. Cortisol is intended to be released for short-term action. The result of long-term stress is like a cortisol gas pedal without a brake, which compromises the immune system. Cannon wrote about stress as a trigger for uncontrolled hormonal secretions that would disrupt internal systems causing disease.

Two decades later, Hans Selye, the Hungarian-Canadian endocrinologist developed his seminal ideas of what was later to be termed ‘stress’. While working on lab rats he made the discovery that any stimulant or stress would trigger the same chain reaction. His work became a game changer. Until that time it was thought that specific diseases led to a specific pathology. Selye found that in every disease stress played a role, in some cases a pivotal one.

He later refined his terminology by referring to the causes of stress as stressors and divided them into three groups: positive, negative and distress.

So what has all this got to do with chickens? Plenty. If we believe Selye (and we should) stress plays a role in every disease and chickens are no exception.

Are aware that two-thirds of the global population have been exposed to the Herpes Simplex 1 virus? Before you wrinkle your nose and confuse it with its cousin Simplex 2, it’s just a fancy name for cold sores. Some people don’t get infected or have cleared the virus; some carry the virus but don’t know it because they’ve never had an outbreak; others rarely have any evidence of it, while still others are plagued with a few every year. Most folks, including me, picked the virus up in childhood and still carry it.

We know that cold sores are often triggered by stress, but that doesn’t mean every stressful life event culminates with an outbreak. We don’t always know why some pathogens get transmitted or expressed in particular people, but not others. The same is true for chickens; but stress if often the catalyst or trigger that sets that pathogen in motion.

It’s important to understand how stressors can affect both our own health and that of our flock.

So what are stressors for chickens?

• Transport
• Dehydration
• Fear
• Reordering of the pecking order
• Scares or attacks by predators
• Overcrowding
• Competition between roosters
• Over mating of hens
• Competition for nest box or roost bar space
• Poor ventilation
• Unsanitary conditions (ammonia build up, muddy runs)
• Changes in feed, improper feed
• Illness in the flock
• Fluctuations in temperature; heat stress; being chilled
• Boredom
• Hormonal changes (i.e. puberty)
• Exposure to toxins or pathogens
• Parasites
• Too much, or not enough, light
• Over handling
• Being chased

Impacts of Stress

• Chicks can have issues with pasty butt, pecking, failure to thrive, smaller size and if it occurs at key stages of development there may be lifelong impacts lasting into adulthood
• Decreased egg production, smaller egg size
• Fertility issues
• Bullying
• Feather Picking
• Pecking
• Cannibalism
• Decreased resistance to pathogens

I’ve never purchased feed store birds. I’ve always obtained birds from local breeders, friends or hatch my own. It’s tragic that chicks are churned out in large numbers in hatcheries, then shipped long distances during which they are overcrowded, hot or cold, trampled or dehydrated. They arrive at a store, where some employees are knowledgeable, while others are not and are housed in less than ideal conditions. It’s no wonder that so many of them die during the first few days or weeks due to being stressed. Instead of going back to the source for a replacement chick when one dies we should be demanding better care of vulnerable birds so they not just survive, but thrive.

Once those chicks settle in they are often in for more stress in the form of new additions to the flock. I might not be popular saying this, but the most common stressor for chickens is changes in the flock dynamic: moving into or out of a flock or having new members added.

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Picture this: you live in a big house with three roommates. You all get along and things are running smoothly until something happens to one of them (e.g. they move, die or get picked off by a predator). Your landlord decides to move a few more tenants in without asking you. You might not like them, but even if you did it will require time getting to know them. There are more of you using the kitchen and bathroom. Just when things are feeling settled your landlord moves in a bunch more tenants – again without consultation – with the theory that you won’t notice, or won’t care or you really didn’t need all that space, did you? Maybe they think it’s not important that you’re compatible with the folks you share your life with.

So the next time someone says get as many chickens as you want, they don’t need a lot of space, they won’t notice it if you introduce them at night or they’ll just work it out, imagine how you’d feel in the same circumstances. Chickens have a social hierarchy, which is constantly being reinforced. Disrupting their stability by adding new members is a stressor with very real impacts on their health.

Chickens carry all kinds of microbes (i.e. bacteria, viruses) as well as parasites in their bodies without getting sick. If their immune systems are robust they are often able to keep those pathogens in check. However, when a bird is stressed the immune system can become weakened and the balance tips so that those microbes or parasites are able to reproduce in larger numbers and make our birds sick. Stressors compromise the immune system so they are more vulnerable to illness  and not able to fight off disease.

If you’ve had chickens for a while you know they don’t like change and have a long list of factors that can stress them. Our job as stewards is to understand chicken social systems, to provide stability and to minimize stressors in order to maximize the overall health of the flock.