If circumstances demand that you change your horses feed, simply doing so outright severely ups the chances that your horse will have a colic or founder reaction. Changes in feed should be done slowly and in small increments. When changing the type of grain your horse consumes, the transition should take about 12 days. Replace 25% of the current feed with the new about every 3 days, until completely switched over. When increasing the amount of grain your horse consumes, researchers suggest increasing the ration at a rate of one-half-pound per 5 days. This is especially important when feeding high-starch diets. Conversely, grain reductions should be done gradually over a one- to two-week period, subtracting about a quarter pound every 3 days. (Because of the size of an average horse’s stomach, 3 pounds is ideally the most it should be fed at one meal.)
When turning horses out onto lush pasture, limit their grazing time for several days to avoid digestive upset and founder. Increase the amount of turnout time by one hour every 3 days until they’re turned out for the desired time (be it all the time or just until they’re brought in for the night). Also, it is a terrific idea for your horses to be full on hay before you turn them out when making this transition.
Remember that we humans have disrupted the way nature intended for a horse to be fed and therefore they are “delicate”. With careful attention to detail we can minimize the chances that we will encounter a problem when changing their eating habits.