The best thing you can do is arm yourself with knowledge.
Horses all react differently to colic-like situations. Some are melodramatic and you would think they are dying when they only have a gas bubble. Others are stoic and will barely let you know how bad it is.
No horse owner should be without banamine, a thermometer, and a stethoscope.
At the first signs of colic, take the horse’s vitals: what is the temp/heart rate/respiration? Elevated heart rate will tell you a lot about a horse’s level of pain (which means you also need to know what is normal for them; <40bpm is the normal range).
Practice listening to the horse’s 4 quadrants of their gut: go back by their flank and listen high near the point of the hip and down low closer to their belly. You should hear rumbles or noise about every 20-30 seconds, or anywhere from 1-3 per minute. If you hear less than that, the gut isn’t moving as it should. It is especially concerning if you hear no noises in any of the quadrants. Also, if it sounds like rushing water, diarrhea is likely on the way. If it sounds like “ping ping ping,” you have excess gas.
Look at the gums: this is one of my biggest indicators of how quickly I will deem the situation an emergency. They should be pale pink, feel moist, and when pressed upon, the pale mark from where you pressed should regain its pale pink color within 2 seconds (capillary refill). If they feel tacky or you have slow refill, there’s a good chance you are dealing with dehydration, which may mean impaction. Mild impactions are often “easy” to resolve on the farm without a vet by encouraging drinking, walking the horse, or putting them in a situation that encourages passing manure (like the trailer). Serious impactions will need a vet and possibly surgery, so you can’t just write them off. You need to be diligent.
If the gums are a color other than pale pink, that is usually a “call the vet now” situation. Pale gums
can mean bleeding or anemia, red gums can indicate shock or endotoxemia, purplish gums indicate cyanosis and you have a serious emergency on your hands.
If the horse’s level of discomfort doesn’t seem too high and nothing on examination indicates an immediate emergency, I will often give banamine and encourage passing manure, hydration, and movement while observing the horse. Often these things are temporary discomfort and resolve.
If I have any doubt at all, I will call the vet for their guidance. Sometimes they may tell me to do the exact same thing: give banamine and observe. Sometimes they may choose to come right out based on the info I provide them.
Just last week I had a colic-like emergency (first one in quite some time) that turned out not to be a colic at all, but a fractured spleen. The horse was hemorrhaging internally. Me being prepared to act in a colic saved her life.