2015 PNER Conference Panel Review – Tying Up in Horses – Part I

Disclaimer: I am not a scientist studying these issues, I’m just a curious individual with enough of an equine science background to make some sense of the biology behind these topics. That, and they fascinate me. Check out this posts internal links if you want to read more into the science behind the tying up disorder.

Exertional rhabdomyolysis (ER) has been recognized in horses as a syndrome of muscle pain and cramping associated with exercise (in some form). This disorder is commonly known as “tying up” when the symptoms are evident. There are two general categories of ER: sporadic and chronic. Sporadic tying up is due to management issues including overwork, nutritional deficiencies, and other environmental triggers. Chronic ER arises from genetic abnormalities that are then triggered to cause episodes of tying up.

ER is being explored in Arabian and part-Arabian endurance horses right now, as much of the previous research has been done in other breeds and sports with differing demands on our equine partners. At the PNER Conference this year, Dr. McKenzie presented current research on the subject of tying up research in Arabian horses (and half Arabians). She is involved with the research herself and had a lot to say about the tying up disorder in general and the work determining the causes of tying up found in endurance horses. Generally, the research has focused on determining a cause of chronic ER in endurance horses, as the causes for sporadic ER are universal for horses (but still important to consider, of course).

I have never personally had a horse with any kind of tying up symptoms, but I’ve seen a good friend struggle with chronic tying up with their Quarter Horse. It can be devastating, particularly when you see a beloved horse in pain and can do very little to help them.

Tying up is the broad term for muscular breakdown and the symptoms that arise from that breakdown. Muscle damage releases potassium and myoglobin, which are then filtered through the kidneys. Since these byproducts are toxic, tying up can lead to kidney failure and death. 

Symptomatically, a horse that is tying up will be stiff and sweaty, not want to move, and will display signs of acute discomfort. 

What I found particularly interesting is that there is not a single cause for tying up. Different causes have taken on different names, but they are all related to the same kind of symptoms and results in the equine athlete. Research has already uncovered several routes to the disorder, and new studies point to even more possibilities that need further exploration.

One thing we do know with some certainly: tying up has a strong hereditary component, but the symptoms can also arise from overwork and other management issues that have already been mentioned.

The apparent causes of tying up in Quarter Horses and Thoroughbreds:

Most of the research into ER/tying up has been done in Thoroughbreds and Quarter horses. In Quarter Horses, chronic ER is usually due to a condition called polysaccharide storage myopathy (PSSM), while in Thoroughbreds it seems to be related to an abnormality in how their muscles contract.

In Thoroughbreds, where about 5-9% of the population has chronic ER, research has established that various stressors show a positive correlation with the disorder’s symptoms. The horse having a nervous temperament correlates to them being five times more likely to tie up. Having a high caloric intake (especially if it’s starchy intake), being lame, and having a period of rest in their recent history (even if it’s only two days) are other factors that trigger episodes of tying up. The chronic ER disorder in Thoroughbreds also appears to be genetically dominant and is therefore easily passed on to the offspring.

It’s suspected that chronic ER in Thoroughbreds is caused by a calcium regulation defect. Since one of the results of this abnormality (other than tying up symptoms) is that the horse can relax and contract their muscle faster than a normal horse, chronic ER in this breed has probably been selected for accidentally. Yes, it’s entirely possible that horses with ER may run faster!

Chronic ER affects around 9% of Quarter Horses and related breeds, like paints and appaloosas. In these types of horses tying up is caused by PSSM. PSSM is, in simplified terms, a muscle-glycogen storage disorder. 80% of affected Quarter Horses have a mutation of the Glycogen Synthase I gene (GYSI) which regulates this storage. The common complaint with PSSM is that symptoms of tying up appear when the horse is exercised after a period of rest – and it does not necessarily have to be hard exercise in these horses. (I think it’s interesting that around 36% Belgian draft horses have PSSM, as well, so it’s not just a disorder found in Quarter Horses and their related breeds.)

As with Thoroughbreds, PSSM is also genetically dominant. It was probably also selected for accidentally in these breeds, because it helps the horses gain weight quickly, and the trend in breeding Quarter Horses is for thick-bodied animals. Luckily, PSSM can now be tested for in breeding animals and hopefully avoided altogether.

Last time: Deli’s rehabilitation update.

Next time: 2015 PNER Conference Panel Review – Tying Up in the Arabian Endurance Horse – Part II

Deli’s big rehabilitation update – and saddle fit issues.

So Deli?

She’s doing pretty darn good, all considering. As I believe I’ve mentioned the “new” barn, which is just someone’s backyard barn, not a fancy “boarding barn”, is a huge step up from the kinds of things I’ve seen while boarding my mare the past couple years.

Her rehabilitation is pretty much at the “build up strength” stage. We have only been stalled somewhat by the dreaded problem of saddle fit issues. That, and the weird as heck weather this winter. It is winter, right?

I am going to share something that makes me cringe somewhat. I like seeing a smooth finely muscled and healthy horse as much as the next person. But I’m going to share photos of my horse, who is out-of-shape and coming back from what is, in reality, at least two years of rehabilitation and rest from various injuries.  Never the same injury, mind. She has yet to re-injure any of her specific soft tissue problems, though her right hind is a huge weak spot for her since this leg has been hurt in various respects. It's not particularly pretty, though SHE is the prettiest creature to walk this good green Earth. Obviously.

So first, a photo of her the day after we moved to the new barn about a month and a half ago (we were still in solid re-hab phase then, coming back from that horrific bite injury):

She is not standing on particularly even ground in this shot but observe the more swayed back, the pointing hind end, and general discombobulation. I am very happy to be away from the previous barn because the hay was no good, she was being harassed and beaten up (and the barn staff didn't care), and she wasn’t in a field big enough (or dry enough) for me to be very happy about it. This horse needs lots of room to move. Don't they all, though?

Deli is a VERY high-headed horse (courtesy of that Saddlebred in her, I’m sure), and her conformation does predispose her to a sway back. My vet was right in saying that just hand-walking and lounging her wasn't going to help develop her back muscles. When I'm riding I’d really like to get on top of building her top line this year because she is turning 16(!) and will be officially over the hill. Sort of. She’s still an Arab so I’m fully expecting her to live and be happy well into her 30s.

Next, a photo taken just a couple days ago:

I think she looks better. Her topline is more filled in, though it obviously needs work. She's also a better weight, a testament to having better quality hay and more room to move.

One thing I can’t help but notice when compared to much older photos of a very fit Deli: more of a dip behind her withers. This is something I have been fighting against a lot lately: the problem of her current saddle combined with her big laid back shoulder and very far forward heart girth. Yes, I use a contoured girth. Yes, I have tried SEVERAL types.

Another reference picture.

 My County dressage saddle has been with us for a long time, but I’m coming to accept that both our conformation has changed over the years (and various injuries to both of us) such that it may not be viable for much longer. This, and the change in our sport-focus (from dressage to trail and endurance riding) makes the saddle less suitable. Yes, I know many people do endurance in a dressage saddle, but for long term I want something that spreads my weight out more, is more comfortable for me (this saddle is REALLY really uncomfortable if I’m in the saddle for more than 5 miles. Like, crotch bleeding uncomfortable), and does not have the continuing issue we have with fighting fit issues caused by Deli’s forward heart girth and big laid-back shoulder. Ideally I'd want something that would still allow me to ride in a dressage-y position, balanced with legs underneath me. And I definitely need something I can get into a comfortable half-seat or two-point in, because that's how we canter these days.

I do have another re-flocking planned very soon to see how much we can get this saddle, which was custom made for Deli and I around seven years ago, to stay good for us at least in the short term. Because saddles? Saddles are expensive. My lovely mare was one of those fabled “free horses”. No such luck for my saddle! And used, without being specially adjusted for Deli, probably isn't going to cut it.

I’ve recently tried several other brands of saddles, including a Tucker and Startrekk (which is treeless). Neither fit well, in large part due to that forward heart girth issue. She’s going to need something with forward-set billets or other special rigging to accommodate this conformation. After sitting in one at Convention, I am coveting the Specialized Eurolight. The idea of being able to tweak saddle fit as Deli changes shape is very appealing to me. As is something that stays comfortable for me on the long miles of trail I'd very much like to ride.

The Startrekk before we started work. That girth crept even further forward.

In the meantime I have been doing more “strength training” than under-saddle work. This involved free lounging Deli over small x-rails (to build her hind end) or with her neck stretcher. I have also been riding her some with my Skito bareback pad, which has helped me realize that my seat is still good and I don't experience pain in that situation. But riding Deli bareback much isn’t great, as ideally I want more between me and her back. 

I’ve lost 30 pounds from my top weight, which is great, but I’d still like to lose 15-20 more before really getting into endurance riding. Luckily it is coming off slowly but steadily – the healthy way. (As an aside, thank you to all the lovely people who commented on how good I looked at the PNER Conference; I never see it because I look at my boring face every day.)

Deli isn’t back sore yet, but I care too much to push to the point that she would be. Her health and happiness is the most important thing. With the upcoming re-flock I’ll also ask the saddle fitter to see if anyone is interested in my awesome dressage saddle. It’s an unusual size (County Competitor 18” and XW, with knee blocks custom made for someone with long legs). Is anyone interested? It’s an awesome saddle, and I won’t be able to afford something new until I sell this one.

Along with bareback riding, I also threw on some new tack which may help with the forward-girth issue at some point: a crupper. This is a piece of tack new to me, and it requires a back-center D-ring – which my bareback pad has but my saddle does not. Deli could have cared less that it was there regardless of how tight it was or whether I was tugging on it at the time. That’s not too surprising as she LOVES having her tail massaged and pulled (it’s a stretch for their spine).

Bootyful.

 She really does love having her tail pulled. The above photo is also a good reference so that I can SEE how much even her croup is. After the fall and bite, her right hind croup was  somewhat atrophied. Consistent programmatic (boring!) work has improved that leaps and bounds and she is much more comfortable all around now.

Deli is headed in the right direction. I'd much rather worry about saddle fit issues than her being injured and in pain, you know?

And she's happy and healthy and my own barn anxiety has faded. Now I just get to enjoy our bond, whatever the world has in store for us next.

Last time: the physiology of exercise and warm-up in horses.

The physiology of exercise and warm-up in horses.

Here are my notes – with my own comments peppered within – from the enjoyable panel at the PNER Conference 2015 put on by Dr. Erica McKenzie BSc, BVMS, PhD., DACVIM, DACVSMR. Yes, that’s a lot of degrees.

This is the kind of stuff I nerd out on regularly anyway, building on my equine science background. I highly recommend my fellow nerds and wannabee nerds dip into the nitty-gritty of horse physiology and nutrition. It prepares our equestrian athletes for whatever we ask them to do, and makes us better horse people.

The long and short of it: horses are better athletes than humans. They have massive lung fuel, which increases the maximum rate of their oxygen use. They have a large heart comparable to body size and have a higher amount of blood hemoglobin (for carrying oxygen to tissues). They have something called a “contractual spleen”, which essentially allows them to squeeze blood out of their spleens and increase their blood volume during exercise. Wild, right? Horses are also efficient at heat loss through sweating. They sweat a lot, and the ability to shed heat can be a limiting factor for some horses.

A recently sweaty Deli, still in her winter woolies.

A horse’s physiology, including their “fragile” stick-legs among other things (their shoulder contraption is a beautiful work of evolutionary engineering), give them a very energy efficient gait. (Especially when compared to me, because my conformation isn’t great.)

However, when it comes to exercise physiology the source of fuel is central to everything else!

Horses have slow digestion compared to other animals. Endurance racing requires a ton of fuel. Dr. McKenzie enlightened us as to one point: a horse can’t have enough fuel for an endurance race just based on recent food intake. They will need to run on stored fuel to be successful.

Muscle, which can be 55% of an athletic horse’s body weight, is the primary storage of glycogen. When glycogen is burned for fuel, waste products like lactate build up and cause muscle fatigue.  Glycogen is primarily used in the absence of oxygen in the muscles – anaerobic situations. Endurance is largely an aerobic sport, where the horse is (ideally) able to intake enough oxygen to not swap to burning primarily glycogen. Instead, these horses will burn fat to fuel their activity (and horses are built for this, so it’s groovy). This is the reason endurance horses are usually fed high-fat low-sugar diets!

One point I found particularly notable in this panel is that to use fat as fuel, a little glycogen still needs to be burned to keep the fat burning process working! So yes, sugars have their uses for an endurance athlete even if fat should be their primary fuel source (to prevent muscle fatigue). It takes horses a long time to replace lost glycogen in the muscles. If you want to read further on this subject, this article on muscle-glycogen replacement in horses was fascinating (and references the more detailed scientific article).

I’m sure you can see how respiration relates directly to where the horse is getting their fuel and a horse’s ability to take in air can be a limiting factor. However, lung volume (unlike heart rate) is non-responsive to training – as in, a horse’s lungs have a cap on how much oxygen they can breathe in. It’s still a HUGE volume of air!

An equine athlete’s fitness level is also is key in how a they burn what fuel they have. The more fit our partners are, the more slowly they go anaerobic and start using up their glycogen stores. Blood volume also increases when you get fit so that you can afford water loss from sweat. And a decrease in the resting heart rate in a fit equine indicates a larger heart that more efficiently pumps blood. Interestingly, max heart rate is not variable and actually decreases as an equine ages.

So what are the practical applications for this information?

First, horses have higher thermal demands than humans – they lose a lot more electrolytes in sweat and their thirst response is not good. Dr. McKenzie recommends you offer water to your partner right when they stop because there may be a small window within which they feel thirsty. This is also why supplementing electrolytes is so common in endurance races.

Second, training and conditioning plays a huge part in improvement. When exercise starts they are always anaerobic to get the whole process started – which is where an easy warmup comes into play. The more fit a horse is the more slowly they use up muscle glycogen stores.

Third, to avoid bonk/fatigue, avoid using up the fuel stored in your partner’s muscle! It’s also a good diet to give them some time to replenish their fuel stores before asking them for another “race” effort.

Last time: what do you pack in your vet bag?
Next time:  Deli’s big rehabilitation update – and saddle fit issues.