All five horses are on 24/7 turnout and stall time as they please. Fed grain twice a day, two flakes of hay at night (most of the time), along with the full turnout. The barn has lanes that lead out to their pastures to they can be in their stall whenever, and in their pasture whenever. They need to be walking to keep their intestines moving and working.
That's where stalled horse run into problems. They eat hay standing still all day, in their cramped little stalls, and get no walking done to keep it all moving freely.
After a good rain, and the grass is rich and green, we'll cut out the hay. If all the grass is dead, we'll add extra hay, since their not getting the nutrients from the grass. The grain ration remains the same, except for my show horse who I regulate according to his exercise level.
In south Texas, we have tons of mesquite trees, so we have to rake out the mesquite beans weekly. My show horse coliced pretty badly, and after two vet trips, three gallons of oil, and three days passed he was fine. The mesquite beans are out fear. They eat them, then get a drink of water, the beans expand in their stomachs, and bam. Instant impaction.
Colic, can happen from feed changed too quickly, too much lush grass if they're not used to it, stress, and many other things. There are ways to prevent some cases, but you can't prevent everything. Like mesquite beans dropping from the trees. -_-
"You're just as sane as I am."~Luna Lovegood.