my horse - are these symptoms of steroid withdrawal?

It is not highly likely to be from any kind of withdrawal. Shaking is usually about disturbed muscle or nerve function related to blood chemistries. Your vet should perform blood work to see what is shown.

I assume the horse was on dex or another glucocorticoid, which may have created a very temporary intolerance to glucose. When glucose is rapidly removed from blood, the horse will shake from the effects of hypoglycemia. The nerves and muscles are both susceptible to an infinite number of chemical reactions requiring the presence of the right stuff in the right amounts. When an exogenous (not made in the body in response to the body's "wisdom") hormone is administered, the body has to adjust to its presence. When it is withdrawn, the body has to adapt again. Different bodies adapt more readily than others.

One dose of of a hormone like epinephrine can have a body shaking out of control, where the same dose will produce no shaking in another animal. But epinephrine (adrenaline) and norepinephrine (noradrenaline) are hormones produced in the medulla of the adrenal glands, while the steroids are produced in the adrenal cortex. They function as separate organs, even though they are parts of the same organ.

Glucocorticoids used as antiinflammatories affect metabolism of glucose, which means your horse could be shaking from hypoglycemia (too little sugar available in the blood to sustain normal neuromuscular functions).

The ravenous behavior sounds like it could be related to low blood sugar, which could be related to the treatment, but it's a stretch to assume anything. You still don't have a definitive diagnosis of what caused the initial symptoms, and it is a mistake to assume that the current symptoms are a reaction to the steroids and not a manifestation of whatever caused the symptoms in the first place.

It sounds to me like this is widespread among horses in your area, and the vets are stumped by the cause, and until the horse owners are willing to go the distance to really give vets the go-ahead to investigate for a diagnosis, it is like a game of Russian Roulette.

I would not necessarily be inclined to blame this on the steroids, although it could be, but I would be monitoring and documenting any abnormal behavior and any physical signs or symptoms in order to relate them to the vet with the hope of finding an accurate diagnosis.

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Add...................... I did find one abstract on human research showing prolonged secretion of adrenaline and the related symptoms (shaking, hyper-reactive, etc) following withdrawal after 48 hours of IV administration of dexamethasone, so it could be related. If it doesn't level out in the next day or two, I'd call the vet for answers.

Steroid Withdrawal Symptoms

Dexamethasone Withdrawal Symptoms

You do realize when a horse comes off a layup and starts feeling better they get a bit full of themselves right?

I don't think your horse has turned into a drug addict from 3 steroid treatments. More likely he's just happy to be feeling good again.

Yes, this is most likely from the steroids (guessing Dexamethasone?) though it's not withdraws. It is still in his system. You can expect this behavior for up to a week.