Today we are going to talk about changing your horse's diet. First of all, there is no need to change the diet if the horse is doing well as variety is generally not needed in horse diets. I think sometimes we change their diets because we are concerned about them getting tired of one feed and want to give them variety, but in most cases the horse doesn't really care.
However, if you need to change a horse's diet, it should be done slowly, including grain, hay, and pasture. The horse's GI tract is sensitive to changes in the diet but can accept changes if they are not sudden. The reason change must be performed slowly is the microorganisms in the horse's hindgut are sensitive to changes in the feed as different feeds require different microorganisms for digestion. Abrupt changes in the diet, especially if carbohydrates are changed, can lead to a high pH in the hindgut, which can cause death of bacteria and release of toxins. These released toxins are absorbed into the circulation and lead to endotoxemia, colic, and founder. A recent study out of New Zealand fed six yearling fillies on pasture and six on silage for three weeks, and then the six on silage were transferred to pasture. The microbes from the horses on pasture were different than those on silage and after placing all horses on pasture, it required four days for the microbes to change after the new feed. For this reason, always mix new and old feed and even hay for 10 to 14 days when changing feed. To avoid having to use a new feed, never run out of feed completely so you have to buy a different brand, and always gradually introduce horses to a new pasture.