Stringhalt is not caused by eating dandelions.
There are several diseases that affect coordination and are related to diet. One of them is commonly called 'grass staggers' and that name usually refers to various deficiencies or diseases the horse gets while on pasture.
No one really knows what stringhalt is, ie, exactly what is happening inside the body. Some studies have found lesions on the nerves, but it's never been demonstrated if they are related to stringhalt or not, and some with stringhalt don't have those lesions. There are many theories as to what causes it - all unproven.
My feeling is that it is such a complex series of motions that it may be due to an actual injury to the hind legs, or to a condition of the brain or spinal cord - which would explain why some horses have lesions on the nerves in the legs and some don't. It can occur in any breed, but I've long had the impression that it occurs more often in heavier breeds. THat's led some to believe that the strain on the hind legs is what causes it, and that's why some have looked for lesions right on the nerves of the legs.
Stringhalt basically is a 'disease by description' since the underlying mechanism is unknown.
However, the way the horse acts with stringhalt is very typical, and the consistency of it suggests a single underlying cause.
The horse will lift the hind leg (sometimes both, one after the other, but one hind leg will often seem to be more affected than the other) up and then stamp it down onto the ground. Some believe the stamping motion (rather than whatever causes stringhalt) is what causes lameness, and I've seen stringhalted horses become lame, even to the point of having to be put to sleep.
But some, other than the snatching/stamping motion, never actually seem to be lame or in pain. They may move normally at the trot and canter. They may only take a few odd steps when they first start moving in the morning. They may only do it when backing up. It can be barely noticeable.
Others are seriously abnormal, and they aren't even stable on their feet. They may even sway or fall.
Keep in mind that most horse owners aren't at all good at differentiating between these different conditions.
These days, many people insist ALL these are simply EPSM and treatable by diet. So you will see a bias - people will insist a horse DOESN'T have something that they don't want it to have....
Similarly, there's a condition called 'shivers'. The behavior is a little different - the hind foot is raised very high, the joints all sharply flexed, the leg held up, and it may tremble - the tail may even tremble. The foot isn't always put down hard like it is in stringhalt. Most old timers will tell you that while a few 'shiverers' go on for years with the same mild symptoms, that it isn't unusual to see a shiverer put down by age 7 - they can get very wobbly and it can worsen drastically over time. The mild cases may get quite tense when asked to stand with one leg held up for a time (like for shoeing) but otherwise may go on for quite some time being quite comfortable and useful. The really seriously affected ones, well, they may be put down quite young.
With either stringhalt or shivers, there is no way to tell if a horse will worsen or not. Because of that, most buyers avoid any prospects with even the mildest signs of stringhalt or shivers - there's just no way to tell if they'll stay mild or worsen and have to be put down.
The thing is, a good many people never get their horse properly diagnosed. They call any odd motion of the hind legs, 'stringhalt' and never get it diagnosed accurately. Some of these horses actually are lame from another cause, and could improve if they got the right treatment.
What are some possibilities of conditions owners have mistaken for stringhalt or shivers?
Some of these horses are actually '
Wobblers'. They've injured their cervical spine (meaning their neck) or they have malformed bones in the spine in the neck, so that these bones do not stay where they should. These bones are supposed to make a nice smooth channel for the spinal cord. Like sections of a hose, they have to line up or they damage what's inside the channel. If these bones are not where they're supposed to be, or they're damaged, the bones press on the nerves inside, in the spinal cord. The slightest pressure on the spinal cord will damage the nerves that start at the brain and extend all the way to the hind legs. Wobblers tend to have their hind quarters sway from side to side, and when trying to back up, they are often reluctant to back up, and can 'hunt' for a safe place to set down their hind legs. They may sway or wobble when being made to turn or even, on a straight line. Some of them will sway if someone simply walks behind them and pulls on their tail.
Some of these horses have
EPM, which requires medical treatment. It is due to a parasite that damages the nervous system. It would be tragic if a horse had EPM, and was assumed to have stringhalt and nothing was done, instead of the horse being diagnosed for EPM and treated.
Some of these horses actually have muscle
diseases that could be treated with diet. Their case is really tragic - they could be almost completely normal with a change of diet.
Others have
lameness that could be treated by medication and rest or reduced work.
Some actually have
stifle issues.
Some horses with
tendon or arthritic problems in the fetlock or pastern, will stumble and then 'grab' their hind leg up in the air, making some think they have 'stringhalt'. Another possibility is fibrotic myopathy. In fact, there are a good many injuries and lamenesses that can make a horse look 'wobbly' or hitchy.
The bottom line for me is that since many horses get very poor veterinary care, when someone informs me their horse has 'stringhalt', I am always privately skeotical unless I am sure they've had it properly diagnosed. Stringhalt simply isn't as common as people think it is. There are many diseases and injuries that are much more common than stringhalt.
Stringhalt is even mentioned in a play by Shakespeare, so it's been with us for a long time. But
really common? No.
On the other hand, a good many people will DENY their horse was diagnosed with stringhalt or shivers, because they want to sell it, and if it got around that the animal had stringhalt or shivers, they'd have trouble selling!!!
Attempting to find videos of horses that are properly diagnosed with these conditions, and really have what they are claimed to have -
Shivers:
Stringhalt:
Fibrotic Myopathy(due to injury - no statement here that this animal was diagnosed by a vet as certainly having FM):
This one also stated to have FM:
