Corn, also referred to as maize, is grown in almost all states in America and is readily available to horse owners. Dent corn, also referred to as field corn, is common in livestock feeds. While low in protein and many of the essential amino acids, corn is the only grain with high carotene content. (Remember that carotene is converted to Vitamin A in the small intestine.) Corn is high in energy density (1.54 Mcal digestible energy/lb) and has a high volume weight (56 lbs/bushel), but it is much lower in fiber and higher in starch than oats. Feeding a volume of corn thus provides a horse two to three times more energy than that same volume of oats. The starch in corn is lower in digestibility in a horse’s small intestine than is the starch in oats, so there is more risk of undigested corn starch passing through the foregut into the hindgut. It is essential that corn be fed correctly to reduce the risk of grain overload in the diet.
Processing corn will increase its digestibility; however, finely-ground corn can cause colic and founder. Corn fed to horses is usually cracked, steam flaked or rolled. While any feedstuff can be overfed, there is a particular risk with corn because of its high weight and starch content. Horses that are obese, insulin-resistant, or prone to laminitis should not be fed corn. Draft horses often fall into those categories. In addition, corn is easily overfed if substituted volume-for-volume for oats.
However, if quality corn is fed correctly, that is, fed by weight in a balanced diet with adequate roughage that fits the requirements of the horse, corn is a safe feed for most horses. In the past, it has been economical to use corn as at least part of the energy composition of a grain mix because the price has been lower than that of oats.Currently there is concern that as the market for biofuel sources increases, high corn prices will not only limit the use of corn as an energy source in livestock diets but will drive up the price of all feeds used for livestock production.
The mycotoxin fumonisin can infect the corn kernel. When ingested by the horse in significant amounts, fumonisin causes a neurological condition termed equine leukoencephalomalacia (ELEM), also known as moldy corn disease. ELEM causes the degradation of the white matter of the horse’s brain, resulting in blindness, coordination problems, and death. Fumonisin-contaminated corn is more prevalent in states with warm, humid climates during the growing season. Horses will readily eat contaminated corn since the fumonisin toxin doesn’t decrease the corn’s palatability. Most horses diagnosed with ELEM ate feed contaminated with corn by-products such as corn screenings. The Food and Drug Administration (FDA) recommends that corn and corn by-products used in horse feed should contain less than five parts per million (ppm) of fumonisin and make up no more than 20% of a horse’s total diet on a dry-matter basis. In addition, the FDA recommends that corn screenings not be used in equine diets. While fumonisin can be detected in the field, it tends to be localized in stalks within the field and thus can be overlooked in field checks. Therefore, corn should be tested for the presence of fumonisin prior to being used in equine diets. Check with your grain elevator operator or feed dealer to make sure that the corn used in your horse’s diet has been tested for fumonisin contamination.
The take home message is that corn can be safely fed to most horses and is usually a cheaper grain energy source than oats. However, due to the risk of moldy corn, corn should only make up 20% or less of the horse's diet.