Whether it’s the grain, hay, or time on pasture, any change in the horse’s diet should be spread over several days or weeks. Increases in the amount of grain given to a horse should be added at approximately 0.5 pounds per day until the desired amount of grain is reached. Grain increases may be necessary because of an increase in activity level or for a mare during lactation. If the grain amount is increased too quickly, colic or founder may occur.
When introducing a new type of hay or grain to a horse, the new hay or grain should replace the old feed at a rate of 25 percent every other day, taking a total of six days until the horse is completely on the new feed. Feed intake or eagerness to consume the diet may decrease during this changeover period. If this occurs, more time may be needed for the horse to adjust to the new feed.
When a horse is to be turned out on pasture all day, especially if the pasture is lush and green, time on pasture should be gradually increased to avoid overeating, in a manner similar to increasing the grain. Horses should be provided with all the hay they want to eat about a week prior to the start of complete pasture turnout. The time on pasture should be increased by one hour each day for four to five days. Then, before the horse is going to be turned out completely on pasture, a hay meal should be provided. It is important to remember that each horse is different. Some horses take more time to adjust to dietary changes than others. Therefore, it is important to monitor the horse’s eating habits and health status carefully during this time.
Craig Wood, University of Kentucky