PSSM1

[Doc-t]

PSSM is still a mystery in horses because, in type 1, there is a confirmed genetic mutation that causes an abnormal construction of glycogen. However, there are other causes of PSSM with similar signs (muscle cramping) caused by, as yet, other reasons other than the genetic mutation of PSSM 1. For now, these other causes are listed as Type 2.

I have heard from some owners of PSSM type 1 horses that when feeding SBM, these horses become too excited, almost unable to handle them. I don’t know if these were heterozygous or homozygous for the mutating gene.

Some people are discussing the role of calcium in muscle contraction and the difference between chelated calcium versus free calcium. Chelation is the binding of a mineral (calcium) to a ligand (a carrier molecule). The most common ligands are amino acids. SBM has all the essential amino acids. I am only guessing here, but if horses cannot access their glycogen for fueling the muscles but now there is more chelated calcium for contraction, horses may start to feel more exciteable.

This, in a way, confirms that these horses are protein deficient. But it places owners in a difficult position. Their horses need protein but by adding it, the horse becomes exciteable. No one is contacting me on this. They just shut down declaring that SBM almost killed them through their upset horse! There has to be more to this story.

PSSM, like almost every disease out there now that wasn’t common in the 1970s, is now affecting so many horses. A genetic mutation has been discovered, but what caused this mutation? Epigenetics is the study of how genes are altered to express something that is unwanted.

It would be interesting to dig deeper to understand why some PSSM type 1 horses become excitable on SBM. There is a correlation, but is there causation? Is more gluconeogenesis occuring? Are these horses reacting to SBM also taking in more glucose now causing muscle irritated?

So, to answer your question, all horses kept in limited pasture and fed hay are chronically deficient in protein. I would try feeding SBM to any horse with PSSM and see what occurs. If no irritation, keep feeding it. If irritated/hyperexcitable, look at what else is being fed that the SBM may be exacerbating. For example, maybe these horses need their hay soaked or have oil added to the diet forcing mitochondrial flexibility (helping the muscle mitochondria use both glucose and ketones for fuel). There is so much room for discovery here. But with no treatment and therefore no source of income for vets or feed companies, where will the reserarch come from? Therefore, the only way to learn is from all of us trying and then reporting, asking questions, and trying again.

Thanks for your question and being an advocate for horses. Together, we will figure this out.

[user1657335136]

Thank you for this response. It gives me much to think about.

Yes, PSSM is still largely a mystery. Some horses seems to be heavily symptomatic, and others not at all.