Oh my goodness! Poor guy, but at least it isn't ragwort!
I know a little about it. The name originated from farmers who would work their plow horses heavily and then give the horses the weekend off. The horses would have the same amount of feed given daily, regardless if they were worked. When Monday came around, the horses were bombarded with lactic acid in their muscles. They were in immense pain, with possible trembling, muscle spasm or collapse.
Is this guy used for jumping? What work is he performing? How often? Does he have a large carbohydrate intake?
"Recovery is monitored by the decrease of these enzymes in the
blood. When both fall to normal levels, treatment can be discontinued and the horse can be put back to work. If levels of these enzymes are not elevated in the blood, then problems other than tying-up must be considered.
Emergency treatment includes a pain killer and a muscle relaxant. Your veterinarian may also administer an anti-inflammatory agent. Intravenous fluids are used for dehydration and to help flush myoglobins out of the kidneys. "
What treatment did your vet suggest? Did your vet suggest to alter the amounts of feed given/type of feed?
"Multiple factors contribute to this syndrome, and different horses are sensitive to different conditions. Regular exercise, daily turn out, a consistent low-carbohydrate/high-fat diet, and a stress-free environment may decrease the incidence and severity of tying-up. Feeding the horse balanced electrolytes, vitamins, and minerals--especially vitamin E, selenium, and calcium--is believed to be effective. Preventive measures that reduce stress, reduce potassium depletion, and improve energy metabolism have been used with varying degrees of success. Chromium seems to decrease the effects of stress in nervous horses. Dimethyl
glycine (DMG) increases the efficiency of energy metabolism. Sodium bicarbonate added to the diet as a buffer is helpful in cases of potassium depletion. Dantrolene and phenytoin are compounds used in the prevention of tying-up, but these are not allowed in horses on the race track. "
Personally, I would consider the amount of work he is used for and take a close look at his feed and nutritional intake. I would also suggest exercising him daily, regardless if it is a fun and light hack. If an attack is to happen again, remember NOT to move him as you would with colic! It can make things dramatically worse. :(
But at least you can work with this problem!