The other day I was having a fascinating chat with a client about their horse’s mallenders. Our conversation started with the usual questions, so I steered it towards explaining how, since 2021, science has been leaning towards mallenders being a detoxification issue along the lines of KPU (Cryptopyrroluria). We continued discussing how equine KPU therapy could help reverse it by supporting the liver’s detox pathways.

Then came the curveball question:
“But  WHY does a mallenders horse overproduce keratin? Where does it all come from? And why don’t Thoroughbreds get it?”

A great question! But I’ll admit I was stumped. I didn’t have an answer, but I knew someone who would: the ever-insightful Dr. Christina Fritz, one of my equine mentors who I studied with back in 2021 (as I know many of you have too), and continue to do so. So, I asked her, and here’s a summary of what she had to say.

What causes mallenders in horses - keratin production or toxin overload?

Dr. Fritz started by agreeing that this was indeed an excellent question but acknowledged that there’s still no definitive scientific answer. However, based on her clinical observations in her practice, horses with what we currently assume is excessive keratin production - whether it’s mallenders/sallenders, dry mud fever (not the wet, very sore type), or even flaking skin on the mane and tail - all have had underlying detoxification issues.

Her theory is that these horses are excreting toxins through their skin as an emergency elimination pathway when the liver’s detox system is overwhelmed. This process pulls dead skin cells to the surface, which are naturally rich in keratin. The result? A build-up of crusty/flaky material.

In her experience, addressing the detox issue by re-evaluating the horse's diet to restore healthy gut and liver function (reconnecting the gut-liver pathway, as per KPU therapy) leads to these symptoms disappearing. These days we now know only too well that horses need their hindgut biome in optimum condition, and this is only achieved by a diet rich in grass forage fibre, with absolutely no highly processed or refined feeds. When the liver can then handle its detox job properly, the skin no longer has to step in.

Why the skin?

- the role of skin as a detox organ

This is where it gets even more fascinating. We already know that horses excreting toxins via the skin is a natural metabolic process common in both horses and humans when detox systems are struggling - we’ve covered the subject of itchy skin extensively in our Coat & Skin page.

It's no different for us humans with eczema or chronic skin inflammation, all rooted in a poor gut biome - possibly compromised from birth for all kinds of reasons preventing the creation (or damage to) a healthy gut microbiome, especially if prescribed antibiotics as a child, but then perpetuated by poor diets - ready meals, too much sugar/white flour, not enough fibre, dehydration, and a liver that’s struggling to keep up.

In horses it’s the same - but the skin gets selective:

• Skin oil glands: Toxins excreted here typically cause scratching of the mane, tail, or belly (more on skin oil glands coming up).
• Sweat glands: When toxins escape here, we'll see itching along the sides of the neck or chest, where horses sweat the most.
• Legs: Yes it's a thing. When toxins excrete through the legs, that's mallenders or sallenders. It's a toxin-excretion thing.

And it’s not so much that mallenders-prone horses overproduce keratin; rather, toxins escaping via the skin carry dead skin cells with them, which are naturally high in keratin.

Keratin is what skin is made from, being a protein that makes up a large part of the skin's outer layer, or epidermis, same as hooves and hair. It doesn’t affect TBs because a) they're shorter haired so they have less oil glands, and b) their metabolisms don’t utilise the skin as a toxin excretion route.

Which links us nicely to the next factor. We've all no doubt noticed that mallenders and the dry, scaly mud fever  affect the heavier, more feathered breeds, while TBs rarely suffer. This isn't random. It’s genetic.

Why some horses are more prone to mallenders

- how equine genetics influence metabolism and skin conditions

Draft breeds and other heavy feathered horses have more oil glands in their legs compared to shorter-haired breeds. Meanwhile, ponies like Icelandics tend to detox more through their skin rather than their hooves - they're apparently less lami-prone but more itchy-skin prone. Thoroughbreds? They’re wired differently, rarely showing skin-related issues or lymphatic build-up like draft breeds.

Dr. Fritz suggested this difference may trace back to when humans began selectively breeding horses - around 8,000 years ago. Different breeds were developed for specific workloads and based on what forage diets were available (no processed feedbags then!), which shaped their metabolisms over time.

• Draft breeds - tend to be lymphatic, not fat-prone.
• Ponies, and especially shetlands, natives and Arabs - store fat easily.
• Thoroughbreds - neither lymphatic nor fat-prone.

These metabolic traits explain how we now see different breed-specific reactions to feeds, drugs, and even environmental triggers. German studies conducted on German Warmbloods (who can tolerate poor diets better than most) differ from US studies based on the US Quarter Horses who are genetically closer to draft breeds, who might show metabolic stress on the same feeds as the WBs. Genetics seem to play a huge role, but science is only beginning to understand how.

Where science meets tradition

There’s also a fascinating crossover here between modern science and ancient wisdom. Chinese medicine considers the skin an 'extra kidney' that steps in when the body's natural detoxification systems are overtaxed. The science now backs this up, confirming that toxins can indeed be excreted through the skin, where previously this was denied.

This is why KPU therapy works so well for mallenders, mud fever, and similar issues. By ensuring the gut remains healthy which naturally connects to the liver’s ability to process toxins, these issues can be resolved naturally.

*On a personal note, during the early years with my Connemara, Murf, from 2001 onwards, he regularly suffered from mud-fever and cellulitis each winter. Everything changed around 2006/7 when we transitioned our horses to barefoot and started following the UKNHCP barefoot forum, run by Nic Barker of Rockley Farm. At the time, there was a lot of early-stage discussion and experimentation on mineral balancing, which inspired me to create my own powdered mix for our horses. That was the turning point - no more mud-fever from then on, and we’ve never looked back.

P.S. This experience was the catalyst for creating our EquiVita/VitaComplete mineral balancers - and the rest, as they say, is history!

Looking ahead

For now, the mallenders/sallenders/dry mud fever answers lie somewhere between genetics, metabolism, and detoxification pathways. Research isn’t quite there yet, but it’s catching up - just as it did with laminitis, ulcers, and hindgut health over the last 20 years or so.

Dr. Fritz wrapped up with this thought:

“Who knows - maybe in 10 years, we’ll have a clear scientific explanation for why draft breeds get mallenders, ponies get fat, and thoroughbreds don’t seem to bother with either.”

Until then, supporting liver and gut health with KPU therapy for horses and mineral balancing remains our best tool for managing mallenders/sallenders naturally.

Meanwhile, here's a selection of reviews we've had over the years:

12.2.24 - "I wanted to give you some feedback on your mallenders and sallenders programme. I took the plunge as I was seeing her getting worse than ever this year. In just a month I am half way through and it has cleared up on her back legs completely and on the front there is no red sore skin anymore. I am so happy I can brush her legs without her trying to move her leg or stomp her feet. Thank you so much. Sarah K. 

28.1.21 - "Nothing seemed to work till starting the EquiVita balancer last November. We clipped him last week to clear up the last of the stubborn scabs, but they've all gone - it's all pink skin now where it was thick scabs before!"

13.6.20 - "So far huge improvements in all departments including a traditional who for the first time has no malanders behind his knee . And an itchy coat is now comfortable and no flaky skin. They love the food and I’m confident that everything they are eating is natural, no fillers or nasties in it" Lynn G.

8.1.20 - "Hi I'm currently using Equivita and have had fantastic results (legs now completely clear). Thank you so much for making such a amazing product. Dianne B."