PSSM and Mules

--Julie Porter, Spring Canyon Mule Makers, Onyx, Calif.

This is kind of a long story, so I’ll make it as brief as possible. I’m hoping to receive some input and get some information out there for other mule owners/breeders. There are a lot of folks out there who know us here at Spring Canyon Mule Makers. We take our breeding program seriously and have been in the mule industry for many years.

A few years back, we were offered a papered, foundation bred quarter mare for pretty cheap. The lady who owned her wanted to move, so she was dumping horses. We had another mule friend who lived close and she vouched for the mare. At the time, there was also a gelding involved, so my daughter took him. I kept the gorgeous mare. We bred her and got a mule foal out of her.

In the meantime, we’ve had a bloodline since 1985, that we had when we ran our pack outfit. I decided to breed one of our grade mares for a horse baby. I picked out a stallion and found out the grade mare had an ovarian tumor and wasn’t supposed to be able to get pregnant any more (even though she has since had two more foals). So, I took that breeding and put it towards the foundation quarter mare. She threw a beautiful, big-bodied, great minded quarter filly.

I took the filly every where the first couple years of her life. At two, I started doing some light riding on her. She was easy and went out with the wagons, trail riding, and did a little bit of mountain climbing. She was being a little herd bound, so  I decided to pen her up in a small pipe coral away from everyone. At Christmas 2017, I decided that it was time to start doing a little cattle work with her, so I took her to a local sorting. We got there and she was not acting her normal self. I figured with the change of weather, it was under lights for the first time, (yada, yada) that was why she was acting like she was colicy. So, I pulled the saddle, gave her some banamine and hauled her home. 

She seemed to be fine the next day, but I gave her a couple days off. I got her out and went to take her for a trail ride. We went out the gate and made it a few hundred yards and she started acting weird again. I was thinking maybe she was going through some two-year-old “stuff.” She locked up tighter than a drum. She was sweating, her muscles were shaking, was breathing hard, and wouldn't move. I tried everything to get her to move. I got off of her and tried to lead her on the ground...nothing. It took forever to get her back home. Again, I left her off for a week this time, keeping her in a small pen again. She seemed to be doing OK at this point, so I got her back out to go ride with a friend. We headed up one of our local mountain trails and by the time we climbed the first ridge, she was having problems again. Again, I got off, and started trying to walk her home. This time, when I got home I turned her back out in the pasture. She paced the fence a couple of minutes, then stopped and urinated and it was blood red, and I knew it was time to call the vet.

I talked with him and he suggested a few things, but he needed to check her out. We started running some tests. The first ones came back and it wasn't a UTI like we were hoping. 

With her symptoms, he wanted to run a hair sample on her for the Polysaccharide Storage Myopathy (PSSM) genetic flaw. Unfortunately, she tested positive/negative, which means she carries the gene for the disease and if bred, can pass it on 50 percent of the time. I wasn't even sure what line carried the gene, so I had to do some research on that, as well. Come to find out, it was from that nice foundation mare that we picked up. I had her tested as well and she tested the same.

AQHA has implemented five panel testing requirements for stallions and they're trying to include mares, but so far, that hasn't happened. I did not know these genetic flaws existed until recently. Some that are in this five panel test are pretty extreme.

So, what does this mean? This genetic flaw is showing up in all breeds now, and there are also different variants to this genetic flaw. Each animal has similar problems, but the basics are that during these “episodes,” they shed muscle. It's also been described as “tying up,” and “Monday morning sickness.”

There are forums on Facebook that give lots of information and helpful hints. Some, like our cases, can be “managed” with diet, exercise, and turnout. One of the best things is the horse just needs to keep moving, so being kept in a small pipe corral would mean you would need to exercise the horse every day.

This genetic flaw gets pretty complicated to fully explain here, but there is lots of information online.

Now, to the “mule” side of why I am writing this.

The mare that started all this had recently foaled with a mule foal, so the vet and I decided now would be a good time to test for this flaw on the baby, since I had not been able to find out much information about mules and PSSM. I had even put it out on the Facebook forum. So, we sent in the hairs and he came back with the same positive/negative result.

All those I spoke with on the PSSM forum, including our vet from Bishop Veterinary, as well as a couple of vets from Davis and Michigan State, felt that the mule could carry the gene, but no one can answer the question as to whether mules will exhibit clinical signs. So we are in uncharted waters.

If anyone has a mule that has any signs of tying up frequently, acting “colic-y”, unusual muscle pain, seems to get unusually sore after being kept in a small pen, etc., please have them checked out. We as mule owners and breeders need to due our part and do the research since it doesn't seem to be out there any where. If you suspect one or more of your horses exhibit signs, please have them checked, as well.

I would love to talk with anyone about this. Feel free to contact me at, on Facebook at Spring Canyon Mule Makers, or give me a call at Julie Porter - (760)378-2222.