PSSM & MIM Symptoms- Muscle Wasting

When it comes to PSSM & MIM symptoms muscle wasting is one commonly talked about especially when it comes to MIM horses. But what is muscle wasting and why do PSSM & MIM horses experience this?

What Is Muscle Wasting?

Muscle wasting also known as muscle atrophy is the wasting, thinning, or loss of skeletal muscle tissue

A Warmblood x Thoroughbred gelding with PSSM2 (N/P8) showing muscle wasting

What Are The Causes Of Muscle Wasting?

Immobility, aging, malnutrition, illness, injury, or disease like Cushing’s or PSSM

Why Do PSSM1 Horses Experience Muscle Wasting?

Unlike MIM, PSSM1 is not a degenerative muscle disease so PSSM1 horses are less likely to suffer muscle wasting due to PSSM itself- But despite this there are exceptions to the rule. PSSM1 horses can still experience muscle wasting due to the causes listed above, undiagnosed MIM, or if they keep suffering tying up episodes, repeated episodes of tying up can lead to muscle damage, and eventually muscle wasting.

Why Do MIM Horses Experience Muscle Wasting?

Most variants of MIM (P2, P3, P4 & P8) are Myofibrillar Myopathy which is a degenerative hereditary muscle disease that causes muscle wasting and weakness. With MIM when damaged muscle tissue is torn down, there is an impaired ability to rebuild it, this makes MIM horses more susceptible to muscle wasting especially as the horse already has a weakness, and as the horse ages they lose the function to degrade protein complexes as well as they used to. Muscle wasting in MIM horses can also be made much worse by episodes of negative nitrogen balance.

What Are The Symptoms Of Muscle Wasting?

-Breathing Issues (The diaphragm is also a muscle and can become affected)
-Dull Coat
-Muscles looking tucked up/sucked up to body
-Muscle Dents
-Protruding Bones (usually ribs and hips)
-Rapid weight loss
-Sunken in areas (i.e hips)
-Struggling to build muscle

What Is Muscle Wasting?
Nellie a PSSM2 (N/P3 & N/PX) Thoroughbred mare with severe muscle wasting, here we can see depression, dull coat, rapid weight loss, protruding bones, and sunken in hips

Can Muscle Wasting In PSSM & MIM Horses Be Reversed?

Yes the best treatment will depend on the underlying cause of the horses muscle wasting.

In PSSM1 horses if PSSM1 is the cause of muscle wasting, this can be reversed through correct management of a low sugar, low starch diet to stop tying up episodes.

In MIM horses muscle wasting can be reversed through the supplementation of the 3 essential amino acids (Lysine, Threonine, & Methionine) which are limited in a horses diet, and/or a protein source.

Additional supplementation of Vitamin E can also help reverse muscle wasting, alongside therapy such as physical rehabilitation therapy, electrical muscle stimulation, and therapeutic ultrasound.

The process of reversing muscle wasting can take time- usually many months, and depending on the degree of muscle wasting some PSSM & MIM horses can be left with permanent damage in the form of severe muscle dents, if the dents are deep enough they may remain with them for the rest of their life as the damage in the muscle is to severe to be reversed.

Nellie a MIM (N/P3 & N/PX) Thoroughbred mare after a few months on the PSSM2 diet, we can see the muscle wasting has been reversed and she is now back to peak condition

For more information on the PSSM & MIM symptom Muscle Wasting check out our YouTube video with examples of affected PSSM horses by clicking this link