When Your Mare Changes Overnight: Hormones, Herds & the Biology of Panic

Carol Moreton • 24 October 2025

When instinct takes over- how hormones, stress, and separation can turn calm mares into chaos

You know that sinking feeling when your usually lovely, gentle mare suddenly turns into a squealing, rearing, fire-breathing dragon?


One day she’s all soft eyes and nickers - the next, she’s pinning her ears, squealing at any gelding, refusing to be caught, or crashing into your personal space with hinds at the ready.


It’s frightening, and it can certainly shake your confidence. It can no doubt leave you wondering what on earth went wrong.

If you’re there right now - please know you’re not alone. What’s happening isn’t a personality change. It’s not bad behaviour. It’s biology and emotion intertwined - and once you understand what’s really going on, the whole picture starts to make sense.


I also completely understand this - I’m walking it myself with our 19yo TB mare, Carmen. After moving her from a busy yard of nearly 60 horses to just her and dear old Murf, she unravelled emotionally – pacing, calling, losing all sense of ease, and those hinds coming a little too close for comfort.


I understand this - I’m living it too
After moving our 19-year-old TB mare, Carmen, from a busy yard of nearly 60 horses to just her and dear old Murf, she unravelled emotionally - pacing, calling, losing all sense of ease, and those hinds coming a little too close for comfort.


The hormone storm

Let’s start with the obvious - hormones. And just to remind ourselves:


"Mares are entire animals – as hormonally complex as stallions."

Simple Systems (Oct'25 Newsletter)


No question - their oestrus cycles can create real biochemical changes in the body and brain.

Something else that we might not realise is that as autumn approaches and daylight fades, many mares experience one last big cycle before the winter pause. Their bodies surge with oestrogen, progesterone, and adrenaline, all preparing for the winter slow-down.


It’s pure biology.  Again, they’re not being ‘difficult’ - shifting hormonal turbulence can make even the calmest mare hypersensitive, clingy, or reactive as their internal chemistry is changing gear.


How to help - think less attitude... more adrenal adjustment

  • Keep her diet low in sugar and starch – high-energy feeds can amplify hormone-driven behaviour.
  • Support adrenal balance and calm nervous energy with herbal support like MellowMare.
  • Add Magnesium to help muscles and nerves relax.


But. Hormones are only half the story...


The biology of panic

Imagine being taken away from your home, your friends, your community – and waking up somewhere new, with unfamiliar sounds, smells, and routines. That’s exactly what happens when we move a horse to a new yard or change their companions.


In equine DNA, a herd equals survival. Horses are hardwired to feel safe only when surrounded by their herd – the eyes, ears, and bond to their buddies that keep them alive in the wild.


When that herd disappears, the horse’s nervous system sends a simple but primal message: “I don’t feel safe!


This is biological panic. It’s not a training issue or what some call 'bad behaviour' – it’s pure instinct. The body’s survival instinct is taking charge.


That’s why you might see:

  • Clinginess to one particular horse (the replacement herd)
  • Calling, pacing, fence-running
  • Aggression or rearing when separated
  • Refusal to focus, tension, trembling


Underneath it all, your horse isn’t trying to be dominant or defiant – they’re terrified.


The Mare’s Role in Nature

It’s worth remembering: in the wild, it’s the mares - not the stallions - who lead the herd. They decide movement, safety, and grazing. They hold the emotional intelligence of the group.


This is hardwired into their DNA - whether wild or domesticated.


So when a mare loses her herd or her environment changes, she doesn’t just lose friends — she loses her role, her structure, and her sense of purpose. That’s why some mares spiral emotionally after a move or separation. They’re trying to find safety again in a world that suddenly doesn’t make sense.


The Stress Chemistry Loop

When a horse feels unsafe, her sympathetic nervous system - the fight/flight response - takes over. Adrenaline floods the bloodstream. Heart rate rises. Digestion shuts down. Logic disappears.


And here’s the crucial bit: when adrenaline dominates, calmers often can’t get through. You have to help the body feel safe first, so then the brain can follow.


That’s why layered support works best - helping body and brain exhale together:

  • HarmonyTonic – grounds emotional stress and soothes grief or loneliness.
  • MellowMare – regulates hormonal rhythm, calms nervous energy, steadies adrenal surges.
  • Valerian – a short-term reset button for the tougher days.
  • Magnesium – eases muscular and neural tension, helping switch off fight/flight chemistry.


Rebuilding safety – the real calm

Once your mare’s nervous system begins to feel safe again, the hormones will naturally stabilise and her behaviour will start to soften. But this takes time – often 2–3 months – and your consistency will matter more than any supplement or training session.


Try to:

  • Work with her, not against her
  • Keep her routine calm and predictable.
  • Limit pressure – even pause ridden or groundwork sessions for a while.
  • Offer quiet company and safe turnout.
  • Reward tiny moments of relaxation.


And most importantly – be kind to yourself.


If your confidence has taken a knock, that’s okay. Fear and empathy often live side by side in good horse people. Taking a step back doesn’t mean you’ve failed – it means you’re wise enough to listen.


In summary

Your mare’s scared, hormonal, and overwhelmed – but she’s also trying her best to cope.


Help her by:

  • Calming her biology - MellowMare, HarmonyTonic, Magnesium, Valerian
  • Restoring her emotional safety - companionship, routine, gentle handling
  • Supporting her body chemistry - a balanced, low-sugar diet


When she feels safe, her hormones, muscles, and mind will follow. And when that happens, you’ll both rediscover the calm connection that made you fall in love with her in the first place. 💛


© EquiNatural 2025. All content is original work protected under copyright, and may not be re-published, duplicated, or rewritten for commercial use without permission.


SHOP - Mares

The EquiNatural Blog

macro photo of short winter grass after rain with water droplets
by Carol Moreton 7 December 2025
Winter grass can be surprisingly high in sugars. Learn why drought, rain and cold snaps can trigger laminitis or cold-induced hoof pain, and how to keep horses safe.
Horses standing in a frosty winter pasture with mist rising over the ground on a cold morning
by Carol Moreton 4 December 2025
Winter increases mineral needs, dehydration risk, and colic concerns. Learn how the right minerals, salt, and hydration routines help keep your horse comfortable and resilient.
A bright chestnut horse cantering across a sunlit paddock on a clear autumn day, looking strong, hea
by Carol Moreton 22 November 2025
Discover why true health begins with energy flow, not disease, and how your horse’s vitality depends on finding that perfect balance – the Goldilocks zone.
two healthy horses playing in their pasture on a sunny autumn day, showing strong immunity
by Carol Moreton 14 October 2025
Help your horse detox naturally this autumn. Support the liver, gut & lymph to recharge immunity and build resilience for the winter ahead.
Horses taking shelter from natural tree shade on a hot summer’s day
by Carol Moreton 23 August 2025
New research shows daylight boosts immunity. Discover the importance of why horses need natural light, fresh air, and freedom for health and wellbeing.
Looking out of a tunnel into sunlight, a symbol of recovery from KPU in horses
by Carol Moreton 21 August 2025
Discover KPU (Cryptopyrroluria) in horses - the possible hidden cause behind the “everything’s wrong” horse. Learn the signs, why it happens, and how to support your horse naturally.
upport your horse’s gut health, immunity & resilienc
by Carol Moreton 26 July 2025
Discover how herbs, antioxidants & plant compounds support your horse’s gut health, immunity & resilience – the final chapter of our Thrive & Shine series.
Horse experiencing stress
by Carol Moreton 26 July 2025
Stress quietly disrupts gut health and immunity in horses. Learn how chronic stress triggers inflammation—and how to calm it with EquiNatural’s C.A.R.E. approach.
Healthy ponies playing, indicating a healthy equine microbiome
by Carol Moreton 26 July 2025
Discover how your horse’s microbiome shapes gut health, immunity & mood – and why fibre, not feedbags, is the key to real equine wellness.
Horse sweating in hot weather with flies — gut health connection explained
by Carol Moreton 15 July 2025
Flies swarming your horse? Discover how gut health, sweat chemistry, and detox balance play a key role — and what to do about it, naturally.
More posts