🐴 PSSM – SOMETIMES THE SMALLEST HORSE CAN TEACH YOU THE BIGGEST LESSONS ❤️
Updated: Aug 30
Whenever one of our horses faces a challenge, we try to learn from the experience and share what we’ve learned in the hope that it may help another horse and owner.
❤️ Missy is our tiny Miniature horse, just 6 hands high, around 60 cm, and she has been part of our sanctuary family for nearly 15 years. She came to us as a young yearling after terrible treatment and, once we had helped her through both emotional and physical recovery, she enjoyed a few years of good health.
As she matured, however, we began noticing stiffness, sweating, changes in movement, colic, lameness and laminitis despite meticulous preventative management. Eventually, the pieces came together:
Missy has PSSM!
🐴 WHAT WE’VE LEARNED ABOUT PSSM
Our knowledge of PSSM doesn’t come from Missy alone. Over the years I’ve worked with many PSSM horses through rehabilitation work, particularly horses with physical or behavioural problems that owners were struggling to understand. We also had several PSSM horses come through our rescue centre. Between those horses and nearly 15 years of living with Missy, we’ve gained a great deal of practical experience managing this condition. If what we’ve learned can help another owner recognise what might be happening with their own horse a little sooner, then it is absolutely worth sharing.
🧬 SO, WHAT IS PSSM?
PSSM stands for Polysaccharide Storage Myopathy. It is a muscle disorder affecting the way energy is stored and used within the horse’s muscles. Muscles mainly store energy as glycogen, which is made from glucose. In PSSM1, a mutation in the GYS1 gene causes excessive glycogen to accumulate within skeletal muscle. So rather than saying a horse simply “can’t process sugar”, it is more accurate to say that their muscles have a problem with the way energy is stored and used.
🤔 WHY IS IT CALLED PSSM?
PSSM is simply the established abbreviation for the condition. Polysaccharide refers to a complex carbohydrate such as glycogen, Storage refers to abnormal storage within muscle, and Myopathy means muscle disease. PSSM is therefore a muscle disorder involving abnormal carbohydrate storage.
👀 WHAT DOES PSSM LOOK LIKE?
PSSM can look very different from one horse to another. Some horses experience obvious muscle pain and tying up episodes, while others show much more subtle signs. With Missy, one of our first clues is that she simply slows down. Normally she is our little Energiser Bunny, bright, nosy, cheeky, determined and full of life, so when she becomes quiet and flat, we pay attention. Signs can include stiffness through the hindquarters, shortened strides, dragging or scuffing the hind toes, unusual hoof wear, muscle soreness, lameness, reluctance to move, weakness, twitching or trembling, unexplained sweating, fatigue, tight or painful muscles, tying up episodes and, in severe cases, dark brown or reddish urine. Missy can also experience colic and laminitis as part of her wider clinical picture, but laminitis is not automatically a symptom of PSSM.
🐎 WHAT DOES “TYING UP” ACTUALLY MEAN?
“Tying up” is the common term for exertional rhabdomyolysis. This means that the muscle fibres are becoming damaged, tight and painful. A horse may become very stiff, reluctant to move, sweaty or shaky, and the muscles can feel hard and sore. In more severe cases, damaged muscle releases myoglobin, a protein found in muscle tissue, into the bloodstream. The kidneys filter it into the urine, which can turn the urine dark brown or reddish. A horse who is severely tying up should never simply be forced to “walk it off” and may need urgent veterinary attention.
⚠️ PSSM1 AND PSSM2 ARE NOT THE SAME THING
PSSM1 has a known genetic cause involving the GYS1 gene, and there is a validated genetic test for it. PSSM2 is a series of conditions that does not have the GYS1 mutation and is considerably more complicated. The group of muscle disorders historically placed under the PSSM2 umbrella is still being researched, which is why it is important not to treat PSSM1 and PSSM2 as simply two versions of the same condition.
🧪 CAN YOU TEST FOR PSSM?
PSSM1 can be genetically tested because the GYS1 mutation is known. DNA testing can be carried out using blood or correctly collected mane or tail hairs with roots attached, and the result can show whether the horse has no copies, one copy or two copies of the mutation. PSSM2 is different, and there is currently no equivalent validated genetic test that carries the same standing as the GYS1 test for PSSM1.
⚠️ WHAT ABOUT P2, P3, P4 AND OTHER GENETIC PANELS?
You may see commercial tests referring to P2, P3, P4 and other variants associated with PSSM2 or Myofibrillar Myopathy. Owners need to understand that these are not equivalent to the established GYS1 test for PSSM1. Research into these variants and their relationship with muscle disease is continuing. That doesn’t mean we should dismiss genetic research. It simply means we need to distinguish between a known disease causing mutation and a genetic variant whose significance is still being investigated.
🧬 ONE COPY OR TWO COPIES OF THE PSSM1 GENE: WHAT DOES THAT MEAN?
Every horse inherits two copies of most genes, one from Mum and one from Dad. With PSSM1, a horse can have one affected copy from one parent, which is called heterozygous, or two affected copies from both parents, which is homozygous. PSSM1 is autosomal dominant, which means one affected copy is enough for the horse to be genetically affected. A horse carrying one copy has around a 50% chance of passing it to each foal, while a horse carrying two copies will pass an affected copy to every foal.
🧬 DOES TWO COPIES OF THE PSSM1 GENE MEAN IT'S TWICE AS BAD?
No. Genetics rarely work that neatly. Some horses carrying two copies may be more severely affected, but the genetic result alone cannot predict exactly how badly an individual horse will struggle. Diet, movement, body condition, general health, management and the individual horse all matter too. Our principle remains simple: manage the individual horse, not simply the label attached to them.
🌱 DIET IS A HUGE PART OF PSSM MANAGEMENT
One of the most important things we do when managing PSSM horses is control sugar and starch. We are particularly cautious with pre bagged feeds such as kibbles, pellets and premixes, which can contain sugars, starches and highly processed ingredients. Our feeding philosophy is simple: keep the diet as straightforward and natural as possible, reducing unnecessary sugar and ingredients that may not suit a susceptible horse.
🌾 KEEP THE MAIN DIET SIMPLE
For most horses with PSSM1, the staple foundation should be a suitable low-sugar meadow hay, ideally fed through a slow-feed haynet so the horse can nibble gradually rather than consuming a large amount and then standing without food. Grass can still form part of the diet where appropriate, but we become much more careful when it flushes. Track systems, break feeding, restricted grazing areas or bringing the horse in for part of the day can all help manage intake while still allowing natural movement.
🌱 WHAT ABOUT LUCERNE?
We generally do not recommend Lucerne for the PSSM horses we work with because we have not had particularly good results with it and have seen some horses become more symptomatic after its introduction. Lucerne can also be hidden in products as lucerne meal, including pellets, premixes and some supplements, so always read the ingredient list rather than relying on the front of the bag.
🌾WHAT ABOUT BALEAGE AND HAYLAGE?
We also don’t routinely use baleage or haylage for the PSSM horses we manage. We prefer the predictability and simplicity of a suitable low-sugar meadow hay wherever possible. The simpler the diet, the easier it is to know exactly what your horse is eating.
🥣 YES, WE DO RECOMMEND A DAILY BUCKET FEED
We believe in giving a small daily bucket feed, not to add unnecessary calories, but to provide vitamins, minerals and other nutrients that may be missing from hay and grass alone. Our Natural Horse NZ All in 1 Equine Support is the nutritional foundation we use with our own horses. It provides broad-spectrum vitamin and mineral support, plus prebiotics, probiotics, and a mycotoxin binder, while keeping the carrier feed simple.
🌿 OUR NATURAL HORSE NZ RANGE.
A quick note before we go any further: this is not an advert for our products.
Although you will see quite a few Natural Horse NZ products mentioned below, it's simply because we genuinely use them with Missy and they have helped her enormously. It would be impossible to tell you honestly how we manage her flare-ups without including them.
We developed many of these products because of horses like Missy in the first place, so I’m not going to leave them out just because we also happen to sell them.
🚶 MOVEMENT IS IMPORTANT
Regular movement is an important part of PSSM management, but there is a huge difference between letting a comfortable horse move normally and encouraging movement during a flare-up. When Missy is well, she walks, trots, gallops and plays freely with the herd. When a flare-up starts, and her muscles become tight, sore or fatigued, we bring her into the pens so she can rest, move at her own pace and recover without trying to keep up with the others.
❤️ WHAT WE ACTUALLY DO WHEN MISSY HAS AN EPISODE....
Once Missy is settled in the pens for rest, our focus turns to monitoring her closely, keeping her comfortable and supporting her recovery. She is never isolated and usually has one or more of the herd choosing to stay nearby, which is exactly how we like it. ❤️
💊 PAIN RELIEF
If Missy is uncomfortable, we treat the pain. During a more significant episode, we may use Bute, phenylbutazone, for short-term pain relief, while being mindful of the gastrointestinal risks, including ulceration, associated with longer-term use. Once the acute pain has settled, we often switch to our Natural Horse NZ Devil’s Claw formula. Devil’s Claw is traditionally used to support horses experiencing occasional discomfort and inflammation, so we use it as part of Missy’s ongoing comfort support.
💚 EQUI MAG
On flare up days we also use our Equi Mag, which is our magnesium support supplement. Magnesium plays an important role in normal nerve and muscle function, so it is particularly relevant when we are dealing with muscle tightness, twitching, trembling or abnormal movement. We have found Equi Mag particularly useful as part of Missy’s overall management programme.
🌿 EQUI BALM, EQUI HEAL AND BODY WORK
When the large muscles through Missy’s thighs and hindquarters feel tight, we gently massage them. We use our Equi Balm as a topical muscle rub. It is a gel containing botanical plant extracts and therapeutic essential oils, and Missy absolutely loves having it massaged in. During summer we sometimes keep it in the fridge and apply it cold as a cooling gel over hot, tired muscles.
We also use Equi Heal topically as another muscle rub when appropriate, alongside gentle body work and massage. The aim is to encourage those tight muscles to relax and make her more comfortable. Nothing is forced. If she says no, we listen.
💧 HYDRATION AND SALT
During a flare up we make sure Missy has constant access to fresh water and adequate salt. If a horse has been sweating heavily, hydration and electrolyte balance become even more important. Severe muscle breakdown can require veterinary assessment, blood testing and intravenous fluids, so if your horse deteriorates or develops severe symptoms, don’t hesitate to call your vet.
🌿 VITAMIN E AND MUSCLE HEALTH
Vitamin E supports healthy skeletal muscle and helps protect muscle cells from oxidative damage. Our nutritional products already provide Vitamin E as part of Missy’s daily supplementation, and we also use natural dietary sources such as flaxseed meal and flaxseed oil. Small amounts of Brazil nuts or shelled raw peanuts can also be included as natural whole food sources of beneficial nutrients and antioxidants.
🍊VITAMIN C
Vitamin C is an important antioxidant that helps support normal immune function, tissue repair and the body during periods of physical stress.
We developed our unique Equi-C formula after researching the different forms of vitamin C available. Rather than relying on a single source, we blended two forms of vitamin C with natural rosehips to support horses that need extra nutritional support.
We use Equi-C as a short course during times of increased physical stress, including during Missy’s flare-ups.
🚨 WHEN DOES A PSSM FLARE BECOME AN EMERGENCY?
Contact your vet if your horse becomes severely painful, sweats heavily, trembles significantly, becomes very weak or unstable, is unable or unwilling to move, shows significant dehydration, develops severe colic-like pain or passes dark brown or reddish urine. Those signs can indicate significant muscle damage and that horse needs more than a massage and a supplement.
❤️ KNOWING YOUR HORSE MATTERS
Your relationship with your horse is one of your most valuable tools. You know how they normally move, eat, stand, interact and respond. With Missy, one of our best warning signs is simply that she isn’t Missy. Our bright, nosy little Energiser Bunny becomes slow, and after nearly 15 years with her, that tells us a tremendous amount. Never dismiss those small changes simply because nobody can measure them with a machine.
🥰 AND THEN THERE IS MISSY
PSSM is only one part of Missy’s story. She also lives with dwarfism and metabolic challenges, but you would struggle to find a horse more enthusiastic about being alive. We absolutely adore her, the herd adores her, and even Reuben, our very large herd boss, is completely wrapped around her tiny little hooves. 😂 When she is well, she gallops, plays, investigates, interferes, causes trouble and throws herself into absolutely everything. She has no idea she is supposed to be fragile, and we have no intention of telling her. ❤️
🌈 PSSM DOESN’T HAVE TO DEFINE YOUR HORSE
There is currently no way of removing the PSSM1 genetic mutation, but that does not mean these horses cannot have good lives. The key is learning what your individual horse needs: simple feeding, controlled sugar and starch, appropriate nutritional support, regular movement when they are well and quick support when they begin to struggle. We have managed Missy for nearly 15 years and, although we have not prevented every flare, she has spent the overwhelming majority of that time doing exactly what she loves: living life to the absolute full. ❤️
❤️ WHY WE SHARE THIS
Natural Horse NZ has grown from decades spent learning directly from rescue, rehabilitation and sanctuary horses. We share these articles because we want owners to understand what they are seeing, recognise when something is wrong and feel better equipped to support their individual horse. If Missy’s story helps just one owner think, “Hang on. Maybe this explains what I’ve been seeing…”, then sharing what we have learned has been worthwhile. ❤️
Natural Horse NZ
