Adding vegetable oil to equine feeds or to equine diets has been a standard practice for literally hundreds of years. Old horse traders knew that adding oil could help slick up a horse for sale long before the science of measuring digestible energy was developed.
There are multiple ways that vegetable oils are added to horse diets. A common practice among horse owners is to add various quantities of oil on top of an existing diet. A cup of oil will weigh about eight ounces and contain about 2,045 Kcal. A 500 kg (1,100 pound) horse at light work requires about 20 Mcal or 20,000 Kcal, so that oil would provide about 10% of the required DE per day. For comparison, a pound of oats, as fed, provides about 1,320 Kcal, so adding oil provides a lot of calories in a small package.
A key element to consider in adding oil on top of an existing diet is that oil adds only calories (crude/unrefined oils might also contain some Vitamin E), so it is possible to alter the nutrient to calorie ratios in a diet. With the addition of moderate quantities of oil, this is unlikely to create issues. If a substantial amount of oil is added on top of an existing diet, the diet might not be meeting the horse’s requirements for other nutrients. Corn oil, soy oil, and other vegetable oils can be used for top dressing diets.
Feed companies also add oil to formulated feeds and will declare the minimum amount of crude fat on the tag. This is primarily from the oil in the grain and the added oil if above 3 to 3.5%. A feed that is tagged at 7% will generally contain about 3 to 4% added oil. Internal formulations systems will also calculate the total digestible energy of the feed, w