When we think about equine health, we tend to go straight to the usual suspects – laminitis, ulcers, EMS. The things we see, the things we talk about all the time.

But when it comes to mares, there’s a whole other layer quietly ticking away in the background… and often only getting attention when something goes wrong.

Few things are more frustrating – or frankly, heartbreaking – than a mare who simply won’t hold. Season after season, everything looks fine, and yet… nothing.

And sometimes, sitting underneath that picture, is something called endometritis – inflammation of the uterine lining.

NB. This isn’t a veterinary deep-dive, and it’s certainly not meant to replace the expertise of your vet. But it is a reflection on what we see in practice, the research that’s shaped our thinking, and the patterns that tend to sit underneath the surface.

What is endometritis – and why does it matter?

Now, despite the name, this isn’t quite the same as human endometriosis (which is a completely different and very complex condition). In mares, we’re usually talking about inflammation inside the uterus itself.

Sometimes that inflammation is driven by infection – bacteria or fungi that the uterus hasn’t managed to clear effectively.

Other times, it follows breeding itself. In a healthy mare, inflammation after covering is completely normal – it’s part of the natural process of clearing semen and any contaminants. But in some mares, that clearance doesn’t happen efficiently.

Fluid, debris, and inflammatory by-products remain in the uterus longer than they should, and the inflammatory response lingers rather than resolving. And in quite a few cases, it’s a combination of both.

Either way, the end result can be similar: persistent inflammation, changes to the uterine lining, and over time, scarring (fibrosis) that makes it harder for an embryo to settle and thrive.

So the obvious question is… why does this happen? And this is where it gets interesting – because it’s rarely just one thing.

Yes, there are physical factors – older mares, reduced uterine tone, conformation issues that allow contamination… all of these being well recognised contributors.

But alongside that, there’s the bigger picture we always come back to:

• How effectively can the mare clear inflammation?
• How resilient is her immune system?
• How well are the wider systems supporting her – gut, liver, stress response?

Because the uterus doesn’t operate in isolation – it’s part of a much bigger system. And when that wider system is under strain – whether from diet, stress, repeated interventions, or general inflammatory load – it can influence how efficiently the uterus returns to a healthy, balanced state after breeding or challenge.

Why it often goes unnoticed

The tricky part is that it often flies under the radar. You don’t necessarily see dramatic symptoms. More often, it’s subtle – a mare that doesn’t take… or takes and then loses early… or keeps coming back into season despite repeated coverings.

Which is why diagnosis sits firmly with your vet – scans, cultures, and biopsies helping to build a clearer picture of what’s happening inside.

What does treatment usually involve?

And when it comes to treatment, modern veterinary medicine has a well-established toolkit.

• Antibiotics and antifungals.
• Uterine lavages.
• Medications to encourage uterine clearance.
• Surgical interventions where needed.

All of which absolutely have their place. But… and this is the bit that often gets missed – they’re largely focused on resolving the immediate issue, rather than rebuilding the environment that allowed it to develop in the first place.

(And yes – if you ever come across references to intrauterine kerosene historically being used to strip the uterine lining… you do rather stop mid-cuppa and think “Good grief…”  Thankfully, this sits firmly in the “controversial and not routine modern practice” category.)

The whole-horse picture

This is where a more whole-horse, preventative approach comes into its own, because if we step back and ask a slightly different question – “What would make this mare less susceptible in the first place?” – we start looking in some very familiar directions.

• Nutrition is a big one. A forage-first diet, balanced minerals, and keeping unnecessary inflammatory inputs to a minimum all help create a more stable internal environment. It’s not glamorous, but it’s foundational.
  
  
• Then there’s the gut. We know how closely the gut and immune system are linked. Repeated antibiotic use, stress, and dietary imbalances can all influence that relationship, potentially affecting how well the body regulates and resolves inflammation. Supporting the gut isn’t just about digestion – it’s about resilience.
  
  
• The liver and kidneys quietly come into the picture too. They’re involved in processing hormones and metabolic by-products, and supporting the body’s natural “housekeeping” processes. When these systems are under pressure, inflammatory processes may take longer to settle.
  
  
• And then, of course, our old friend stress – the piece that so often gets underestimated. Social stress, environmental change, discomfort elsewhere in the body… all of it feeds into the hormonal and immune picture. A mare who is constantly on edge is not in the best place, physiologically, to regulate inflammation efficiently.

Prevention – stacking the odds in your mare’s favour

So when we talk about prevention, it’s not about a single supplement or a quick fix – it’s about stacking the odds in the mare’s favour.

Supporting her from the inside out so that:

• her immune response is appropriate and well-regulated
• her body can clear inflammation effectively
• and her internal environment remains as balanced as possible

Because that’s ultimately what influences whether inflammation resolves… or persists.

A final thought

There are no guarantees with reproduction – there never have been. But what we can do is shift the foundations.

Work alongside veterinary care where needed, while also strengthening the areas that conventional approaches don’t always address.

Over time, that combination – patience, good management, and a whole-horse view – can make a meaningful difference.

If you’re navigating challenges with your mare – or simply feeling like something isn’t quite adding up – you’re not alone. These situations are rarely as straightforward as they first appear, and often there’s a bigger picture quietly sitting underneath.

If you’d like to step back and make sense of what might be going on, our From Confusion to Clarity page is a good place to start. It walks you through the common patterns we see, and how to begin approaching things in a more structured, whole-horse way.

And as always, you’re very welcome to get in touch – sometimes it just helps to talk it through.