I don't know if this is any help. it's more feed related I suppose, but it is my only experience of horses who suffered from this and it is second hand:
A guy I know who does endurance and I discussed this once. I was interested to know why he fed his horses a low sugar, high oil diet and he told me it was in order to prevent tying up. His horses were almost skinny but heavily muscled and did a lot of exercise. Previously he had fed the horses a diet fairly high in grain products and had problems with tying up, particularly with his mares, resulting in him having to withdraw from competitions in the early stages and seek vetinary attention . Following recommendations from his vet he found reducing the grain element of the diet and adding (unmolassed) sugar beet for slow release energy and oil for more calories worked wonders. He also stopped feeding alfalfa except after hard exercise, something to do with it having too much protein and calcium which effects the levels of something (
) in the blood which causes cramps and tying up. Apparently mares are more prone than males, due to their hormones!!
The vet did say about changing my geldings diet, he tied up last night 20 mins into a ploddy hack, we'd only been walking too! He is quite a stressy thing though, am thinking a dog set him off, (they seem to like to chase/snap at him), he turned himself inside out and then completely switched off, sweating buckets. The vet said about the high fibre diet, but alfalfa came up as a thing to feed him, but i did wonder about the protein levels. Everything i have found so far is exactly what your endurance guy says, so that is good to know. Trust my ginger gelding to get something mares are prone too!
we have a 4* horse who is prone to tying up. we had a lot of help from baileys feeds. we couldn't feed him hardly anything without him tying up, we were really worried as we were up to 3* level on pony nuts, but knew we couldn't continue. starting from the beginning we think his tying up was triggered by grass that had been fertilized, so now he is never allowed to graze anything that looks like rich grass at home or at events. caroline at baileys put us on a programme of outshine and stud balancer plus his horse and pony cubes! and now touch wood he has only had a few minor setbacks over several years now. Blood tests show he has a naturally high whatever it is in his blood anyway. he had a minor 'do' 2 weeks before burghley but jumped beautifully clear round there so it is possible to manage. hope this is helpful.