Horse | Changing Diets
The horse’s diet (type of forage or grain, or the amount of either) should be changed gradually over several days or weeks. Increasing the amount of grain fed at a rate of no more than about 0.5 lb (0.2–0.3 kg) daily until the desired level is reached is a safe approach. Increasing the amount of grain fed too rapidly may cause colic or founder. It is also best to gradually decrease the amount of grain fed, particularly for horses on a high-grain diet, such as those returned home from strenuous performance training or competition. Their diet and amount of exercise should be reduced gradually over a 2-week period.
When given a day off, horses normally subject to strenuous daily exertion should have their grain decreased that day, be given some exercise, and preferably stay in an enclosure of sufficient size to allow them to run. On the first day of work or training following the day of rest, they should be warmed up slowly to prevent exertion myopathy.
When either the type of hay or grain is being changed, replace only about 25% of the current feed every other day so that it takes about 1 week before the new feed completely replaces the old. Many horses prefer the feed to which they are accustomed, so when the type of feed is changed, feed intake or eagerness to eat may be reduced unless the new feed is substantially more palatable than the old. Horses being put on lush, green pasture should be given all of the hay to which they are accustomed before being turned out on the pasture. If possible, increase the time the horses are on the pasture by 1 hour each day. After the 4th to 5th day, they can be left on the pasture. The more lush and plentiful the pasture forage the more important these procedures.
This article is from "Feeding and Care of the Horse", second edition, by Lon D. Lewis, Lippincott Williams & Wilkins, 1995. Reprinted with permission from the publisher.