Chronic Stress in Horses

Contents

1. Stress isn’t the problem. Getting stuck there is.
2. Does this sound like your horse?
3. Stress is not just a feeling
4. Meet the body's emergency response
5. The bit we've been missing - recovery
6. The horse who's tired but wired
7. Stress and the gut - now things start getting really interesting
8. What about adrenal fatigue
9. So what does recovery actually look like?
10. A final thought

"Healing is a process that always starts with stabilisation. Until the body's stable it cannot heal. The body then needs to clear out the roadblocks and get the nutrients that it needs to repair itself. When you have this combination in place the body can truly begin to heal."

Dr Nuzum, Toxicologist, Doctor of Naturopathic Medicine

Stress isn’t the problem. Getting stuck there is.

If there’s one thing I’d love you to take away from this page, it’s this: Your horse is supposed to get stressed. Really.

Stress itself isn’t a disease. It’s not evidence that something has necessarily gone wrong – although of course it could also mean that, but not always. The point I’d like to make here isn’t about wrapping our horses in cotton wool so that nothing remotely challenging ever happens to them, because…

A healthy stress response is one of the cleverest survival systems the body has.

Take our old friend – the pheasant that launches itself out of the hedge. Horse instantly decides it is, in fact, a ten-headed winged predator intent on eating them alive. Heart rate rises, attention sharpens, energy becomes immediately available, muscles prepare for action, digestion temporarily becomes rather less important because, biologically speaking, finishing breakfast can wait until we know whether we're about to become breakfast.

Then the pheasant disappears. Nothing ate anybody. Horse snorts, stares after it, possibly gives you the look suggesting that it was you who completely failed to appreciate the seriousness of the situation...

And gradually the body settles again. Heart rate comes down, muscles soften, attention widens, digestion carries on, and the nervous system moves from mobilisation back towards recovery.

This is stress working exactly as nature intended.

The interesting question isn't therefore, "Does my horse get stressed?" Every horse does. The much more useful question is: "Can my horse recover from stress?"

Because that's where chronic stress begins to look very different. And once we understand that distinction, a great many horses who seem anxious, explosive, grumpy, withdrawn, tired, ulcer-prone, gut-sensitive or simply not quite themselves begin to make much more sense.

Does this sound like your horse?

A chronically stressed horse doesn't always look "stressed". This is important – because some horses become increasingly obvious about it, while others become increasingly quiet, and at the deeper end some hit shut-down.

You might recognise:

• always on edge, jumpy, scanning or easily startled
• tense muscles, bracing, or difficulty relaxing
• rushing, freezing, spinning or becoming unusually reactive
• difficulty concentrating or coping with something they previously managed
• repetitive behaviours such as box-walking, weaving or cribbing
• fussy eating, appetite changes, bloating or altered droppings
• poor sleep or reluctance to lie down
• weight or condition changes
• becoming increasingly defensive around handling, grooming, tacking up or rugging
• withdrawn, flat, disconnected or apparently "shut down"
• losing curiosity about things they once enjoyed
• that almost indefinable feeling that the light has gone from their eyes

None of those signs diagnoses chronic stress on its own. Meanwhile, pain, gastric disease, lameness, neurological problems, nutritional insufficiency and many other physical conditions can produce overlapping behaviour. But taken together, these signs can tell us something enormously important.

The horse may be struggling to regulate – and that's where I'd like to start.

Stress is not just a feeling

When we humans use the word stress, we tend to mean the emotional experience – "I'm stressed." "Work's stressful." "That traffic was stressful."

But biologically, stress is much bigger than a feeling – it's an adaptive response. Something changes, internally or externally, and the body adjusts in an attempt to cope.

The trigger might be obvious – a predator, separation, pain, a new yard, transport, competition, a frightening or traumatic experience.

Or it might be more in the background – ongoing discomfort, poor sleep, inconsistent feeding, lack of movement, social insecurity, continued low-level pain, too little forage, unpredictable handling, or simply living in circumstances where the horse has very little control over what happens next.

The whole body adapts – the nervous system hits the alert button, the endocrine system responds, immune signalling changes, the gut reacts, and the brain learns.

And for a while, that's exactly what we want it to do.

Meet the body's emergency response

Let's bring our pheasant back.

The moment your horse perceives potential danger, information travels rapidly through the brain and autonomic nervous system.

The sympathetic branch becomes more active, the adrenal medulla releases adrenaline, and the hypothalamic-pituitary-adrenal – HPA – axis becomes involved, eventually influencing cortisol production.

Meanwhile heart rate increases, blood pressure and blood flow change, glucose and other fuels become more readily available to fight or fly, attention narrows onto whatever might matter for immediate survival, and muscles prepare to move.

The body has effectively said: "Something important is happening. Resources this way, please." Digestive activity can change, as can immune signalling. And this is brilliant biology.

We used to talk about cortisol and adrenaline as though they're toxic chemicals the body would be much healthier without. They're not. We couldn't function properly without them.

Cortisol helps regulate metabolism, energy availability, immune activity and normal daily physiology, while adrenaline gives the body the rapid mobilisation it needs in an emergency.

The problem isn't that the body produces stress hormones. The problem comes when the system has to keep adapting again... and again... and again... without sufficient opportunity to return towards baseline.

The bit we've been missing – recovery

For years, conversations about stress focused heavily on fight or flight – and understandably so. It's dramatic and easy to recognise.

Horse sees monster. Horse prepares to run. Lovely neat biology lesson.

But fight/flight is only half of a healthy stress response – the other half is recovery after the event.

The nervous system should be flexible. It should be able to mobilise when necessary... and settle when the threat has passed. That's what resilience really looks like – not a horse who never reacts, but a horse who can react appropriately, recover, and move on.

Let's think about that for a moment. A nervous system that can move between states is fundamentally different from one that repeatedly struggles to do so. One horse experiences the event, responds, recovers. Another experiences the event... but something lingers. The next event arrives before the body has fully settled. Then another, and another...

Eventually the system starts behaving differently.

The danger has gone... but the body hasn't got the message

This is where chronic stress becomes much more interesting than simply saying, "The fight/flight switch got stuck on." Because biology isn't really an on/off switch – it's a constantly adjusting network.

A horse exposed to repeated stress may begin changing how strongly they react, how quickly they react, and how effectively they recover afterwards. The brain learns from experience, while the autonomic nervous system, hormonal signalling, immune signalling and gut activity all adapt. Even perception can change.

A horse who has repeatedly experienced pain when being saddled may eventually react before the saddle is even placed. Or a horse repeatedly separated from companions may start responding to the earliest signs that separation is coming. And a horse whose environment feels unpredictable may become increasingly vigilant because, from the nervous system's point of view, vigilance helps keep them safe.

This isn't the horse being stubborn or misbehaving – it's prediction. The brain has learned that last time something happened, something bad followed, so it prepares earlier next time. Which is very clever... right up until the prediction itself becomes part of the problem.

The horse who's wired...

This is the stressed horse most of us recognise – eyes wide, head high, banana neck, muscles tight, startles easily, always watching, can't settle, seems permanently "on".

They might rush, spook, become difficult to handle; their threshold for reacting becomes smaller and smaller, and things they once coped with suddenly seem enormous. The nervous system is essentially behaving as though danger might appear at any moment. But the horse isn't choosing that state – their biology has decided that vigilance is currently the safest strategy.

But there's another horse – the one that's gone quiet. And I think this one is missed far more often.

They're not exploding or leaping around the yard. They're quiet, maybe very quiet. They're compliant but not offering much, staying where they're put, perhaps disconnected from the world around them. Absence of an obvious fight/flight reaction doesn't automatically mean absence of stress.

Behavioural science has taught us to be cautious here. Horses experiencing chronic frustration or repeated inability to escape aversive situations can show increasingly passive responses, and absence of conflict behaviour alone doesn't prove that the horse is comfortable.

Sometimes the system doesn't get louder – it seems to get quieter.

And when a horse loses curiosity, engagement, appetite for life or normal responses to their environment, I think we should listen every bit as carefully as we do to the horse bouncing around at the end of the lead rope - because shutdown is not necessarily "calm. And that distinction matters enormously.

Which horse is more stressed?

Here's the frustrating answer – we can't always tell by looking at one hormone.

Cortisol has traditionally been treated almost as though it were a stress thermometer: higher cortisol = more stressed; lower cortisol = calmer. Except biology, inconveniently, refuses to be quite that tidy because cortisol changes naturally through the day.

Exercise can affect it, something new can affect it, individual temperament and previous experiences all matter.

Studies looking at equine stress regularly find that physiological markers don't always agree with one another – or with behaviour. This is why modern welfare assessment increasingly looks at patterns across behaviour, physiology and context, rather than expecting one cortisol reading to tell the whole story.

Which brings us back to something I've learned to trust enormously over the years: the horse's story.

What changed, when, and what else was happening? What does the horse do before, during and after the event? How quickly do they recover? What's their appetite like, their gut, sleep, relationships, movement, pain status? The pattern often tells us far more than one isolated number ever could.

And this is where adaptation becomes everything

There's a wonderful biological concept called allostasis. Don't panic – I'm not about to make you memorise it. 😉

Homeostasis is the word most of us know – it describes the body's continual effort to maintain a reasonably stable internal environment: temperature, blood glucose, fluid balance, pH... all the countless variables that need to stay within workable boundaries for life to continue.

Allostasis adds another layer. Instead of asking: "How does the body keep everything the same?" it asks: "What does the body change in order to keep everything working?"

And that is stress biology in a nutshell.

If it's cold, metabolism adapts; if food is scarce, energy use adapts; if danger appears, the nervous system adapts; if pain persists, movement adapts; if the environment feels unsafe, behaviour adapts.

The body is astonishingly good at this - which explains something horse owners see all the time. A horse can appear to cope for a very long time.

Coping costs something

Imagine the body has a biological bank account – every challenge requires a withdrawal.

Ordinarily that's fine. Stress response? Withdrawal. Threat passes → recovery → money goes back into the account. No problem.

But imagine the withdrawals keep coming:

• poor sleep
• pain
• social stress
• restricted forage
• transport
• new yard
• another painful episode

And meanwhile, recovery isn't putting enough back in.

Eventually the horse may still look as though they're coping... but the account is running increasingly low. That's the essence of what scientists mean by allostatic load – the cumulative biological cost of repeatedly adapting to challenge.

And this is one of the most useful ways I've found to think about chronic stress. It isn't necessarily one terrible event - sometimes it's simply... too much, for too long, with too little recovery in between.

Then one tiny thing happens, and suddenly everybody says: "But he's coped with that for years!" Exactly. He may have – until he couldn't.

The final event isn't always the event that created the problem. Sometimes it simply tips a system that's been adapting for months or years beyond its current ability to compensate.

That's why we can see a horse apparently managing perfectly well... then suddenly struggling after a yard move, a companion leaves, a period of box rest, an illness or injury, a competition season, a dietary change, or something apparently as insignificant as a weather shift.

We naturally blame the last thing - but biologically? The better question may be: "What had this horse already been carrying before that happened?"

Now we're starting to understand chronic stress.

So what does a horse actually understand as "safe"?

This is where I think we humans sometimes make life unnecessarily complicated.

We can buy enormous stables, beautiful rugs, the best feeds, the finest tack, the softest bedding... And absolutely none of those things answers the horse's nervous system's most basic questions:

• Can I eat?
• Can I move?
• Can I see and interact with other horses?
• Can I rest safely?
• Can I predict what happens here?
• Can I move away when I'm uncomfortable?
• Does anything hurt?

Horses are social, mobile, forage-eating animals, and research increasingly supports social contact, free movement and access to roughage as fundamental welfare needs rather than optional luxuries. Which doesn't mean every horse needs to be turned loose on several thousand acres of tundra with twenty cousins somewhere on the horizon.

It means we need to remember what kind of animal we're managing.

Pain is stress

This sounds obvious, yet pain is still one of the most overlooked causes of apparent behavioural stress.

• A horse with gastric pain doesn't know they have gastric ulcers, but they know that eating, girthing, moving or being ridden feels uncomfortable.
• A horse with musculoskeletal pain doesn't understand biomechanics, but they know certain movements hurt.
• A horse with hindgut discomfort doesn't know their microbial ecology is having a bad week – they simply know their gut hurts.

So they adapt. Brace, avoid, rush, pin ears, refuse, freeze... Which is why, whenever behaviour changes, one of my first questions is:

"Could something hurt?" And not: "How do we make this horse behave?"

Sometimes behaviour isn't something to correct. It's information.

Stress and the gut – now things get really interesting

Years ago we explained this rather neatly: Stress causes cortisol → cortisol switches digestion off → gut breaks down. End of story. Except the modern picture is considerably more fascinating, because the brain doesn't simply talk to the gut.

The gut talks back. Constantly.

Welcome to the gut–brain axis – or perhaps more accurately, the gut–brain–immune–microbial conversation, because there are rather a lot of participants in this particular group chat.

The brain communicates with the gut through nervous-system and neuroendocrine pathways. The gut sends sensory information back. Immune molecules carry messages. Microbes produce metabolites that interact with the host. Motility, barrier integrity and inflammation all join the conversation. Which means: the nervous system can influence digestive function – and digestive state can influence nervous-system function.

Now we're talking.

Stress changes the gut – and the gut talks back

When the body perceives threat, gastrointestinal physiology can change – motility, secretions, blood flow, visceral sensitivity and eating behaviour can all be affected.

We also know that the equine microbial community is sensitive to stressors and management changes. Transportation and weaning, for example, have both been associated with shifts in gut microbial populations.

So imagine a stressed horse develops altered gut motility. The intestinal environment changes, the microbial community may shift, microbial metabolites change, perhaps the gut becomes more sensitive or uncomfortable, and inflammatory signalling changes.

The nervous system receives that information, and what does physical discomfort tell an already threat-sensitive nervous system?

Something isn't right.

So vigilance increases, muscles tighten, behaviour changes – and round and round we can go.

Stress affects the gut, and gut affects the stress response.

That doesn't mean every anxious horse has dysbiosis or every horse with dysbiosis is anxious – biology is never that obliging. But it helps explain why gut problems and behavioural stress so often travel together, and why sometimes you can't successfully support one without considering the other.

And this is not "all in their head". Nerves are real, as ae hormones, immune signals, microbial metabolites, and pain.

The separation we've historically made between "mental" and "physical" health becomes increasingly difficult to defend once we look at how closely these systems communicate - because the horse doesn't have a mental self and a physical self. There's just... the horse.

And yes, the microbiome and immunity are in there too

Now obviously you knew I wasn't going to get this far without mentioning microbes. 😉

Horses rely heavily on their hindgut microbial population to ferment fibre and produce metabolites that contribute to their energy economy and intestinal environment. That microbial ecosystem also interacts with the gut lining and immune system, and we now know it's influenced by diet, medication, age, management, disease and stress.

But – importantly – we still have plenty to learn about what a universally "healthy" equine microbiome actually looks like.

I rather love that uncertainty because it brings us back to one of our favourite principles: Don't obsess over one bug – look at the environment - diet, fibre, diversity, movement, medication history, stress... the whole ecosystem.

The same applies to immunity. Rather than stress simply "switching the immune system off", acute stress can temporarily alter immune activity as part of a normal adaptive response, while chronic stress can disturb how that signalling is regulated. Which brings us back to that word again: dysregulation.

Not exhaustion, nor a broken system. A system that's been adapting for so long that its regulation may no longer be working as elegantly as it once did. And that matters because regulation can change again.

What about "adrenal fatigue"?

Yep, this is one of the phrases I used myself for years.

It made intuitive sense – horse under chronic stress, adrenal glands continually producing stress hormones, eventually the adrenals must become exhausted. Except that's not really how modern stress physiology understands the process - the adrenal glands don't simply run out of cortisol.

What's changing is regulation across the whole stress-response network – brain, autonomic nervous system, HPA axis, immune signalling, metabolism, behaviour and feedback systems. So when we see that familiar tired but wired picture, I now try hard not to think: "The adrenals are exhausted," but instead: This entire system has been trying to adapt for far too long.

A subtle change, but a really important one.

Tired and wired

You probably know this horse – you may even have felt it yourself!

They're exhausted, but they can't properly relax. Movement is tense rather than fluid. They may appear lethargic one minute and dramatically reactive the next. Appetite can become inconsistent, rest disturbed, they're easily tipped over threshold, and small events produce surprisingly large responses.

It's tempting to think: "How can you possibly be tired AND wired at the same time?" Very easily, as it happens.

Being hypervigilant is exhausting. So is maintaining muscle tension, repeatedly mobilising energy, being in pain, not resting properly and living with disrupted gut function. Eventually there may be less and less reserve left for anything else - and this is where the basics really matter.

Quality rest and sleep. Appropriate social contact. Forage. Movement. Predictability. Physical comfort.

Not glamorous, but profoundly biological.

Food is nervous-system biology too

A horse standing without forage doesn't know that their owner is restricting calories because their condition score is 7/9." All their biology knows is: "There is no food."

For a species designed to eat fibre across almost all of the day, prolonged restriction changes more than calorie intake. It affects the stomach, hindgut, foraging opportunity, routine and predictability – and the stress response too.

Which is why "stress management" can never simply mean adding a calming supplement to the feed bowl. We have to look at the life around the bowl.

So what does recovery actually look like?

After all the nervous systems, microbial metabolites and HPA axes... the horse doesn't need a lecture. The horse needs conditions in which recovery becomes possible.

Enough appropriate forage, rest, movement, social contact, routine and predictability, physical comfort...

Repeated often enough, these become messages that the horse doesn't need to be on guard every second. Which brings us back to Dr Daniel Nuzum's quote at the top of this page: "Healing is a process that always starts with stabilisation."

Despite everything we've learned since, that fundamental idea still resonates with me - because you cannot bully a stressed system into wellness. If a horse is hurting, frightened, sleep-deprived, nutritionally depleted, socially distressed and digestively uncomfortable, throwing an expensive bag of nutrients into them isn't fixing the foundations. We must stabilise first.

Stage One: Stabilise and Alleviate

Look for what may be keeping the alarm system busy.

Pain? Gut discomfort? Environment? Forage? Social stress? Poor sleep? Unpredictability?

Reduce unnecessary load wherever you reasonably can.

Stage Two: Restore the gut conversation

If digestive function has become caught up in the stress cycle, support it. Not because "everything starts with the gut", but because everything is communicating – brain, gut, immune system, nervous system, endocrine system and microbiome. Sometimes supporting the gut changes behaviour. Sometimes making life feel safer improves the gut. Same horse, same network.

Stage Three: Support the body's housekeeping systems

Once the horse is more stable, consider the systems handling the ordinary metabolic workload of living – liver, kidneys, lymphatic circulation, blood flow and cellular energy production.

I still like the word detoxification, provided we're clear what we mean.Not vague toxins mysteriously floating around the body, but the perfectly normal physiological processes through which the body transforms, transports and excretes metabolic waste and foreign compounds.

Support the foundations gently rather than trying to force some dramatic "cleanse".

Stage Four: Fortify

Now feed the horse – properly! Quality forage, appropriate fibre, adequate protein, forage-balanced minerals, salt, essential fatty acids and plant diversity where appropriate - because regulation and repair cost nutrients.

This is where we start putting something back into that biological bank account.

Then support adaptation

Targeted herbs and nutrients may help support nervous-system resilience and appropriate adaptation while those bigger foundations are being addressed.

And give it time

Because recovery isn't something we do to a horse. It's something the horse's body does when we give it enough of what it needs...

and remove enough of what keeps getting in the way.

A final thought...

If you've reached this page because your horse seems anxious, reactive, shut down, exhausted, gut-sensitive or simply not quite themselves, please don't read all of this and think: "Good grief, my horse's whole nervous system is broken."

That's not the message at all. In fact, I think the recent insights of understanding stress give us far more reason for optimism than the old model ever did, because we're no longer talking about adrenal glands that have been "used up" - we're talking about an adaptable biological system. And adaptable systems can learn new patterns.

The nervous system can experience safety. The gut can restabilise. Microbial communities can change. Pain can be treated. Management can change. Relationships can change. Nutrition can improve. Recovery can happen.

Stress isn't the enemy. The goal isn't to remove every stressor from your horse's life – we couldn't even if we wanted to. The goal is to help the horse meet life's ordinary challenges, and find their way home again afterwards. That's resilience.

Every horse’s story is different - but the pathway back to balance is always the same: stabilise, rebuild, fortify. With the right support, even the toughest cases can turn a corner.

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