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Jax’s Story – PSSM in Horses, Symptoms, and Promising Tips for Management

PSSM in horses - PSSM management, PSSM symptoms, muscle disorders and myopathies in horses

Jax’s current genetic results are n/P1, n/P2, n/Px – what exactly does this mean??

PSSM in horses: each PSSM gene, both the Type 1 gene and the experimental Type 2 genes, are inherited in twos – one from each parent.  The “n” stands for a normal allele – a gene that is not defective.  “n/P1” means Jax is heterozygous positive for the PSSM1 gene defect – he has PSSM1 (Polysaccharide Storage Myopathy) as it is a semi-dominant gene (as opposed to recessive, which needs two genes to be active). 

New genetic testing has come out for PSSM2, though the tests are still experimental in nature.  According to Jax’s results, he’s also heterozygous for a PSSM2 gene that is linked to Limb Girdle Muscular Dystrophy (P2) and for a gene associated with RER (Recurrent Exertional Rhabdomyolysis).  Basically, he has a perfect trifecta of muscle disorders. (Click here for more on testing for PSSM).

Some signs and symptoms of PSSM in horses:

  • Sticky stifles
  • Sore back, hindquarters, shoulder, neck muscles – chiro/massage short-lived.  See A Look at PSSM – What Chronic Pain Feels Like
  • Behavior changes
  • Possible feed/gut complications – colic episodes
  • Hoof pathology and low grade laminitis
  • Muscle atrophy and wasting
  • Gait changes and abnormalities, including cross-firing, bunny hopping canter, twisting hind limbs, tightrope walking
  • Postural changes and strange swellings
  • Difficulty lifting hinds for farrier
  • Skin sensitivity

Above: Jax, May 2019 – Management is really starting to work! He has had full test results and hybrid management for approx. 1 year. Note that in late 2015 he had all of the PSSM symptoms mentioned above.

What can be done for these muscle disorders and myopathies?

PSSM1 is a sugar storage disorder – the muscles overstore glycogen, which can cause spasms and tie up at the extreme, and stiffness and behavioral changes on the lesser end of symptoms.  Basic management practices are lower sugar intake – hay instead of pasture, low NSC feeds, and higher fat content for energy (to make up for lack of carb intake and to get the horse to use fat as fuel instead).  Vitamin E, magnesium, and other supplements can really help these horses.  

PSSM2 is a muscle wasting disorder – there are several genetic variants/issues grouped under this umbrella term, and Jax’s particular variant is the same gene affected by Limb Girdle Muscular Dystrophy in humans.  PSSM2 horses tend to go into Negative Nitrogen Balance (NNB) easily – basically their bodies will start to catabolize muscle to make up for the lack of protein (PSSM2 horses need VERY high protein levels to sustain – I use Pea Protein Powder from Bulk Supplements). 

As they fall further into NNB, they will get more symptomatic and may lose the ability to stand (meaning once they’re down, that’s it).  High protein diets and work to keep muscles strong (but not enough to overwork them) is the best management practice for these horses.  

I’m still looking into RER and what exactly it entails, but it seems to affect the central nervous system rather than the muscles.  Management for these horses include small amounts of fat as a calm energy source, calming supplements, low stress environments (though they can handle stressful situations with the right training!), and a chance to run/sprint and work off pent up energy.

Getting a diagnosis for PSSM1

This can be difficult, as many vets are unfamiliar with PSSM in horses, and the symptoms can mimic so many other issues (Lyme, EPM, hoof pathologies, and so much more!).  My journey to getting a diagnosis for Jax was a long one – it took over a year to get the PSSM1 diagnosis, then another 2 years to test for the experimental PSSM2 variants.  It took all of that information to find the right management for him, so it took almost 3 years to get a good management that works.  To see how we progressed from first symptoms to diagnosis of PSSM1, see my Horse Health posts:

Getting genetic testing results for PSSM2

After PSSM1 diagnosis, which I got through Animal Genetics in Florida (I’m in the US), Jax kept having bouts of muscle loss.  On the PSSM Forum (Facebook) the term Negative Nitrogen Balance (NNB) was being used, and the description fit Jax perfectly. 

I then learned that NNB doesn’t affect PSSM1 horses like it does PSSM2 horses (all living beings go through NNB from sickness or other issues – it’s what makes you feel weak after the flu – but PSSM2 horses can go into NNB and not come out of it, getting weaker and catabolizing more muscle as the protein deficit continues to grow).  It was at this point, after 2 years of having a PSSM1 diagnosis and still struggling with management, that I decided to test for PSSM2 through Equiseq

High protein and letting muscles rest are two major considerations for PSSM2 management, and it was after hybridizing my management style for all 3 – PSSM1/2/RER that I finally really started seeing major results.  The company that tests for these genes is Equiseq in the US, and CAG in Germany has also picked up the tests for customers outside the US.  These tests have not yet been peer reviewed, but the sheer number of people who have tested and managed their horses based on these results speaks volumes, and I encourage anyone interested to read through Equiseq’s site and join the FB group! (Click here for more on testing for PSSM).

Physical Management Techniques (exercise, massage, myofascial release):

These are the physical management techniques I’ve used to build Jax’s muscles back and get him to a healthier state.  It took quite a long time, and wouldn’t have worked without dietary management as well, but was integral to getting him healthy again. 

Treeless, bitless, and barefoot work best for Jax – holding the bit makes his jaws sore, compensation patterns overwork his shoulders and cause saddle fit issues with rigid structures, and metal shoes cause splints due to Jax’s tightrope walking and forging.  Here’s a link to my posts concerning tack and equipment we’ve tried and either loved or sold on:  

Some important notes on feed

Electrolytes are extremely important for PSSM horses.  An electrolyte imbalance can cause even non-PSSM horses to tie up, so imbalances can severely effect a PSSM positive horse.  See my notes on electrolytes here:

A Disappointing Change in Facilities and Management Issues in 2018

Jax needs forage 24/7 – his high protein needs and sensitive stomach means he should never be left with an empty stomach.  In late 2017 to early 2018, the boarding facility started letting the hay run out in his drylot (along with some other issues). 

By mid 2018, it was becoming a serious problem – I could count every vertebrae in his back, and despite me feeding my own hay and talking with the barn owners nothing was being fixed.  I ended up moving him back to his old facility, which also stopped feeding enough hay (to be fair there was a hay shortage, but I wasn’t paying board to let my horse starve) – Jax ended up getting moved to a friend’s house for a month until another boarding facility opened in November of 2018. 

This facility only had pasture, so until I could secure my own land and get what I needed we had to make adjustments and make the pasture board work.  I found with high protein, he could sustain on pasture, but it wasn’t ideal.  Clovers triggered electrolyte issues, so while I’m finding he can handle pasture it has to be the right kind of pasture – not lush, clover-heavy fields. As you can see, PSSM in horses can be a balancing act!

The very definition of Negative Nitrogen Balance – he’s being fed enough to hold most of his weight, but his back muscles are melting away – click for a larger pic to count the backbones along his spine…  

One thing to note here – while other horses were also losing weight, none were losing it like this, and none of them were being fed extra hay by their owners.  This muscle loss was exacerbated by his genetic issues.

Dietary PSSM Management While Boarded On Pasture Nov ’18 – Aug ’19

While on pasture Jax needed a LOT of support.  I think the movement from grazing and Vitamin E from grass was great for his muscles, but the high potassium, and possibly sugars, were not.  He needed:

1 pound of Renew Gold, 1 cup chia seeds, 4 cups of pea protein (double what he had been getting, I use Pea Protein Powder from Bulk Supplements), AZ Copper Complete (see my post on AZ CC), Horsetech’s MMX and Gutwerks, 3 tbsp magnesium oxide, up to 4 tbsp iodized table salt (salt counteracts potassium which is high in fresh forage, more on that later), 2 tbsp baking soda, and a huge selection of herbs both fresh and powder to support various systems. 

Keep in mind he was still healing during this time, so the herbs may have been helping the healing process rather than the pasture issues.  However, the extreme amount of protein was essential while on pasture – without it he had blood in his urine and muscle wasting (Negative Nitrogen Balance).  I also had to add back in some canola oil for additional fat about a month before I moved him home.

On pasture, and just getting over a fairly symptomatic and potassium-triggered spring season. Notice the very tight muscle in his hip and lumbar pain is a constant issue, but overall he is holding weight and doing well.

Trialing a Grain Free Diet After Moving Home, August 2019

Jax’s diet during this time was completely grain free, and was a mash of: 1 cup chia seeds, 1 medium carrot chopped into tiny pieces, 1.5-2 cups pea protein isolate (I use Pea Protein Powder – CLEAN from Bulk Supplements), Horsetech’s AZ Copper Complete, Horsetech’s MMX (for extra magnesium and B vitamins), Horsetech’s Gutwerks, 1.5 tbsp magnesium oxide, 1-2 tbsp iodized table salt, and 1 tbsp baking soda

I also added a handful of fresh herbs including oregano, parsley, rosemary, peppermint, and thyme.  This is on top of ad lib grass hay only, as alfalfa contains potassium and seems to trigger him (even small amounts of pellets).  He was also getting grass from his field, but it quickly turned into a mostly dry lot as it was quite small (around 1/3 acre for 2 horses).

After 1 week on grain free – this diet may not have enough protein, but I want to give it a good trial before raising.  For the first time in months, I pulled him out of the pasture and found NO lumbar pain!  Stifles and hips were loose as well! However, notice the focal divot at the junction of shoulder and chest.

Ultimately this diet didn’t hold out, as the protein levels just weren’t enough. I also found that when I added Renew Gold back into his diet (the only grain is rice bran, but still technically a grain) he improved, so once again we’re sticking with the Renew Gold. However, I’ll keep this diet in my back pocket just in case, as he did do well on it for a time.

  • Glycemic Index and the PSSM Horse – Rice Bran and Copra
  • 2017 Year in Review – PSSM Ups and Downs, and the Major Affects of Hooves on Muscles
  • See Jax’s Current and Past Diets (updated March 2020)
  • Some things I’ve learned since writing the above posts are 1) high levels of oil (like the recommended 2 cups for PSSM1) cause IR (insulin resistant) symptoms; and 2) copra is VERY HIGH in potassium and at certain times of year can trigger his electrolyte imbalance issues (usually around spring).  In early 2019, I had to take copra out of his diet completely as it was triggering exercise intolerance and causing him to be trembly in his neck and shoulders (along with other mild PSSM symptoms).  He’s more prone to choke when his neck is trembly, which is why I soak his feed into a mash.  In mid-2020 he seems to handle small amounts of copra on top of his pound of Renew Gold on occasion, but it’s not something I want to add back in full time just yet.
  • Renew Gold has just enough copra, and therefore potassium, to potentially be a potassium issue (which seems to spike every spring).  My “grain free” diet started in August of 2019 was meant to test if Renew Gold may be causing any troubles.  Early 2019 was pretty bad for potassium symptoms and was triggered by clover; late 2019 he was triggered again with symptoms of mild head shaking and aggressive behavior to other horses (started when I trialed small amounts of alfalfa right after moving him).  Two days after removing all alfalfa again, and his demeanor overall was much calmer.  Renew Gold did SO WELL for him for over two years – but if potassium is a trigger (spring 2017 we had to remove alfalfa, spring 2018 we had to remove a supplement with added potassium, spring 2019 we had to remove copra) then at least testing without it is a good idea.  As of early October, I’m adding small amounts back in with no issue, so I think the alfalfa trial was our main (and hopefully only!) issue. Update July 2020: Our yearly spring electrolyte issues caused us to lower Renew Gold down to 1/2 pound daily to limit potassium; since around June he’s gone back to a full pound of Renew Gold daily with no issues – I think being able to sweat out potassium makes a huge difference in whether or not he handles these potassium sources.  He rarely sweats in the summer and never in the winter, and I think because he’s a light sweater he’s prone to raised potassium levels. Update August 2020: What a short-lived update the previous one was! In August he stopped handling all of his supplements. See Jax’s PSSM diet page for more on what’s working for him.
  • Fat can be introduced in the diet in much healthier ways than oil.  AZ Copper Complete (which is in a flax base) and chia seeds have very healthy, high Omega 3 fat.  For horses that have issues with oil, seeds can be a huge benefit! Update March 2023 – flax affects Jax’s hooves and causes lameness, so he’s back on chia seeds as his fat source!

Some PSSM1 management research: 

“…To evaluate the changes in muscle that lead to this energy deficit… analysis revealed enrichment in pathways involving mitochondria biogenesis, oxidative phosphorylation, fatty acid metabolism, glycogen and glucose metabolism…”  Molecular bases of equine polysaccharide storage myopathies.  

“…In the PSSM muscles, histological data revealed… abnormal polysaccharides, inflammation, necrosis, and lipomatosis and active regeneration of fibers… a decrease of mitochondrial number… Extensive accumulation of an abnormal polysaccharide displaced and partially replaced mitochondria and myofibrils…”  Gene expression profiling in equine polysaccharide storage myopathy revealed inflammation, glycogenesis inhibition, hypoxia and mitochondrial dysfunctions.

Some PSSM2 management research: 

Chronic Protein Deficiency In Horses
Amino acid polarity
Amino acid metabolism, biosynthesis, and catabolism

Branched-chain amino acids (Bcaa) and delayed muscle soreness. “BCAA substantially decrease muscle soreness, enhance recovery from exercise and consequently improve long-term performance. See:…”  

Other Dietary Things I’ve tried:

  1. B vitamins
  2. MSM – too much makes his manure smell like sulfur, but overall MSM does seem to help when his muscles are getting too tight for unknown reasons.  I’ve found that MSM reduces his need for B12, and too much of both together can make him spooky!  (Is this due to some methylation issue?).  See my post: MSM for PSSM and muscle sore horses – liver and muscle health
  3. Vitamin E – gives energy, helps with gait abnormalities.  Too much makes him spooky.  Feeding liver detox herbs helped him handle higher amounts of Vitamin E without spooking issues.
  4. Copper and zinc help with a softer coat and muscles, and helps to keep him from fading and sunbleaching – though he still has a drastic color change by fall (from bronzy to very light)
  5. Magnesium – linked to insulin resistance in humans.  High amounts seem to help with hoof health.
  6.  Devil’s Claw Plus and Bute-less are pain relievers that have Devil’s Claw and Yucca.  DCP is more potent and has been amazing for relieving minor symptoms and avoiding banamine use.
  7. Salt – counteracts potassium and an important electrolyte that needs to be supplemented for most PSSM horses – 1-2 tbsp per day is the usual recommendation. Jax does better with access to a salt block but NO supplemental salt.
  8. Baking soda – this is a big one!  This brought back exercise tolerance and canter!  It’s the go-to “medication” for kidney acidosis in humans and horses, and I think kidney support is the main function that’s helping Jax, since his first sign of issues is discolored urine (meaning kidneys are always one of the first systems affected, right behind muscles).

Interesting Links for Further Research: Growth Hormones, Pituitary Involvement, and Mitochondrial Issues:

Gene expression profiling in equine polysaccharide storage myopathy revealed inflammation, glycogenesis inhibition, hypoxia and mitochondrial dysfunctions “…In the PSSM muscles, histological data revealed PAS positive amylase resistant abnormal polysaccharides, inflammation, necrosis, and lipomatosis and active regeneration of fibers. Ultrastructural evaluation revealed a decrease of mitochondrial number and structural disorders. Extensive accumulation of an abnormal polysaccharide displaced and partially replaced mitochondria and myofibrils…”

Enhancement of Muscle Mitochondrial Function by Growth Hormone “…The 4-fold increase in plasma GH caused elevations in plasma IGF-I, insulin, glucose, and free fatty acids and a shift in fuel selection, with less carbohydrate (−69%) and leucine (−43%) oxidation and 29% more fat oxidation…”  NOTE: Leucine is an amino acid that has circulated some PSSM informational sites/forums as being vital to muscles – it’s interesting that the findings in this study saw a decrease in Leucine usage…

Pituitary hormone and insulin responses to infusion of amino acids and N-methyl-D,L-aspartate in horses. “…In the horse, aspartic acid, glutamic acid, and NMA seem to stimulate GH release; arginine and lysine seem to stimulate prolactin and insulin release; and NMA seems to stimulate LH and FSH release. It seems that N-methyl-D-aspartate glutamate receptors are involved in controlling GH, LH, and FSH secretion, whereas other mechanisms are involved with prolactin secretion. These results also indicate that gonadal steroids interact with amino acid-induced pituitary hormone release in adult  horses…”  

Multiple Effects of Growth Hormone in the Body: Is it Really the Hormone for Growth? “…The disruption of GHR in skeletal muscle and the consequent histomorphometric changes in myofiber type and size and myonuclei number result in functionally impaired skeletal muscle. In agreement with these effects, the histology of muscles of untreated GHD patients is strongly altered, and glucose and triglyceride uptake and metabolism in skeletal muscle of GHR mutant mice are affected…”

Regulation of mitochondrial oxidative phosphorylation through cell signaling  “The mitochondrial oxidative phosphorylation (OxPhos) system plays a key role in energy production, the generation of free radicals, and apoptosis. A lack of cellular energy, excessive radical production, and dysregulated apoptosis are found alone or in combination in most human diseases, including neurodegenerative diseases, stroke, cardiovascular disorders, ischemia/reperfusion, and cancer…”

Here’s a couple more articles related to growth hormone, glutamine, and asparctic acid:
Only the last link pertains to horses, the others are on humans and mice. Some of the growth hormone info may point to why studs seem more likely to be asymptomatic.  

Here are a couple of articles pertaining to arginine, the 1st one is particularly interesting for horses suffering from IR, and the insulin/arginine issue may only pertain to mares (see the 4th link):

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