Horse’s Neck, consisting of bourbon, ginger ale, and bitters. Not the one we’re talking about, but still useful.
With any disease condition, including those of the nervous system, you can say that a disease is either congenital, that is, the horse was born with it, or that it was acquired, say, due to an accident, or some sort of disease process (of which there a lot). Of course, there are entire textbooks written on Equine Neurology, and this article is not meant to be that.
Something that’s gotten a lot of recent attention are problems related to the horse’s neck, particularly as those problems relate to how horse’s move. In adult horses, when they have problems in their neck, veterinarians can sometimes pick up signs of incoordination that can affect a horse’s ability to move normally (sometimes easily, sometimes not). Unfortunately, neck problems can be very difficult to deal with.
I think that pretty much everyone has a general idea of what the nervous system is and does, if only because most everyone has had, or knows someone who has had, some sort of an issue with their nervous system, be it nerve pain (e.g., “sciatica”), a major brain issue such as a cerebral hemorrhage (“stroke”), or just a punch in the arm (you can tell it hurts because you have a nervous system). But let’s start by talking about three big things that the horse’s nervous system does for the horse.
NOTE: We’re not going to talk about ALL of the things the nervous system does for the horse. Take thinking, for example. Thinking is a function of the nervous system, but some horses, like some people, seem to use that part of their brain more than other horses. ‘Nuff said.
Anyway, here are the three big things (things that we can tell, anyway).
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You can’t do this without good proprioception!
Proprioception is the sense of body position, movement, and force. It’s an automatic process that allows the horse’s brain to know where his body is in space without relying on his eyes. For a horse to have good balance, and to do the many activities that we ask of him, he has to have good proprioception. With good proprioception, you can easily put an ice cream in your mouth. If you don’t have it, it could end up in your eye.
- Motor function. Motor function is the ability to perform voluntary, skillful, and efficient movements. It’s more than just nerves, of course, normal movement requires the coordination of multiple systems, including the nervous system, the muscles, and the cardiovascular system. But normal nerve function is critical for normal movement.
- Pain is among the most important signals the horse’s body gives it to help him survive. Pain alerts the horse to the fact that he has a nail in his foot, or that an injury hurts. Pain is an alert to the horse that he might want to avoid something harmful, or not use a part of his body that hurts.
A turducken
For the purposes of understanding what happens to the movement of the adult horses when there’s a problem with his nervous system, you need to know just a tiny bit about where the spinal nerve fibers are. The last thing that I want to do is make you endure a lesson in the anatomy of spinal cord fibers, but when it comes to understanding the horse’s nervous system, it’s helpful to have a good idea of their basic orientation. Think of a turducken.
NOTE: For those of you who aren’t in the culinary know, a turducken is a poultry dish consisting of a deboned chicken stuffed inside a deboned duck, and then that combination is stuffed inside a deboned turkey. Outside North America it is known as a three-bird roast. In England, “goodducken” replaces turkey with goose (I have never had this). There’s some dispute about its origin – there’s apparently something similar in a 1913 Spanish cookbook, and that’s all I’m going to say about it right now. But you can order a turducken on-line them if you want to try one.
Cross section of a horse’s neck. You tell me it doesn’t look like a turducken.
In the turducken-as-horse’s-nervous-system model, the chicken represents the pain fibers, the duck represents the motor fibers, and the turkey (or goose, if you’re in the UK) represents the proprioceptive fibers. “Any why,” you might ask, “Do you even bring this up, and particularly around the holidays?”
Here’s why.
When the adult horse’s nervous system gets affected by its various problems, the proprioceptive fibers are the ones most on the outside of the spinal cord, while the pain fibers are the ones deepest (the motor fibers are the duck, in the middle). Since the proprioceptive fibers are the most on the outside, when spinal column problems happen, the nerves on the outside of the cord are the first one got get pressured (“pinched,” as it were). If you’re looking at a horses (whose nerves are getting impacted by the vertebrae of his neck – or worse, riding them – the first thing that you notice is a relative lack of knowledge of where the horse’s body is in space: a proprioceptive deficit, as it were.
Of course, if a horse loses his ability to use his muscles or feel pain, that’s a really big deal, because it means that there’s been a whole lot of damage to the spinal cord. Those problems usually aren’t hard to spot. We’re not talking about those problems – fortunately, they aren’t all that common – but when they a horse loses motor or pain function, the problem is usually more serious.
SO WHAT HAPPENS WITH NECK PROBLEMS?
Mostly, when an otherwise healthy horse – no fever, eating fine, moving well at the walk, etc. – is having coordination problems (e.g., stumbling, or some sort of vague performance problem), one of the first places that we think of looking is at the vertebrae of the neck: the cervical spine. Seven bones make up the cervical spine of the horse. That’s the same every mammal – whales have seven cervical vertebrae, as do giraffes, although, as you might imagine, the cervical vertebrae of the giraffe are really big. The joints between the bones of the cervical spine make the horse’s neck quite flexible, allowing the normal horse to swing his head from side to side and up and down, collecting on request (at least sometimes), or rearing in defiance, as mood determines.
By the way, I found this incredibly cool 3D model of the third cervical vertebrae of the horse which you can see below
Problems related to the vertebrae of the horse’s neck usually end up causing pressure to be put on the horse’s spinal cord because the vertebrae themselves aren’t normal. Those problems occur when the hole in the middle of the vertebra effectively gets too small, either because there is some sort of a constant problem, (this would be what’s known as a “static” compression) or because the problem occurs when the neck moves (this would be a “dynamic” compression). There are any number of reasons why this can occur, such as malformation of the vertebra, or, in older horses, arthritis of the joints between the vertebrae.
One last little bit of relevant anatomy, (I promise, the last). The nerve fibers that run from the brain to the hind legs are the ones that are the outermost in the spinal cord. So, when pressure is put on the spinal cord, the outermost nerves get affected first, and the horse’s ability to know where his hind legs are in space (proprioception) gets affected. And that’s exactly what we can often see.
HOW DO YOU TELL IF A HORSE IS AFFECTED BY NECK PROBLEMS?
How you tell is what a neurologic examination is all about. There’s certainly a little bit of art in a neurologic exam on a horse, but your veterinarian will be looking for subtle signs that your horse is lacking coordination. You usually won’t see anything when the horse is walking – sometimes horses with mild neck problems can even perform. However, they may have trouble doing things like:
Walking normally when their head is up in the air- Walking a serpentine over a street curb (they may miss the curb with their back feet, or hit themselves while trying to negotiate the curb)
- Resisting a pull on the tail. Normally, when you pull the horse to the side by his tail, he’ll brace himself and push back. With neurologic disease, you can pull them to the side more easily – sometimes you can almost pull him over.
- Troubles spinning in a tight circle. Normally, horses are pretty handy, and cross their feet while spinning around you. When the neck is affected, the horse might stumble or hit himself.
- Slow to replace a hind leg when it’s crossed in front of the other hind leg. Some docile horses will stand wherever you put the leg, but if there’s a nervous system problem, you can sometimes cross their legs and they’ll just stay there. They don’t really have a good idea of where their hind end is.
- Neck stiffness or reluctance to turn when asked to turn his head back to the side to get, say, a carrot.
There are other things to look for, as well – a complete neuro exam looks at the whole horse. It takes a bit of practice and experience, too. But if your veterinarian suspects that a horse has a problem with his neck, the next thing is to try to find it.
Normal horse neck X-ray.
HOW DO YOU FIND THE MALFORMATIONS?
Now comes the complicated (and more expensive) stuff. Sometimes X-rays can show a neck problem. X-rays can be tricky, however, because they have to be positioned correctly or you can miss things, or see things that really aren’t there. Ultrasound can occasionally be useful. You can inject dye into the horse’s spinal canal to see if it’s getting pinched off (this is done under general anesthesia at a hospital). You can inject dye and then do a CT scan (well, you can’t, and most veterinarians can’t, but it can be done in certain locations) for even more detail.
WHAT DO YOU DO IF YOUR HORSE HAS A NECK PROBLEM?
This is the frustrating part. It’s really hard to do much because this is a mechanical problem – the horse’s body isn’t working right. What really needs to be done is to get the vertebrae to stop pinching the horse’s neck. Believe it or not, there are surgeries that can be (and are) done to try to stabilize the vertebrae of the neck – they do the same sort of thing in people sometimes, too. The surgeries can achieve some modest success in some horses, but they don’t reliably return an uncoordinated horse back to normal. It’s an expensive surgery only done in a few places.
Other approaches involve trying to relieve inflammation in the horse’s neck. Sometimes that involves injections of anti-inflammatory agents into the neck joints, which, as scary as that may sound, isn’t terribly complicated if you’re using an ultrasound machine to guide the needle. Various oral anti-inflammatory and/or pain-relieving agents can help some horses, too, and, frankly, if you have a horse with a neck problem, I’d try those first. But even in the best case scenario, if you have some sort of a structural defect in the horse, any relief you give him is only going to be temporary. Ultimately, horses with neck problems usually end up getting retired, because they just can’t safely do what’s being asked of them.
TO SUM IT UP
Even though they can be diagnosed, problems with the vertebrae of the neck can be really hard to deal with. Treatment can provide some temporary relief in some cases, but even if you can provide the horse some relief, you still have to worry about getting on the back of a horse that isn’t completely aware of where his body is in space. It’s all very complicated.
