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 8 ounces and contain about 2,045 Kcal (Calories). A 500 kg (1100 lb) 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 may 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 may no longer be meeting the horse’s requirements for other nutrients. Corn oil, soy oil and other vegetable oils may 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 3-3.5%. A feed that is tagged at 7% will generally contain about 3-4% added oil. Internal formulations systems will also calculate the total DE of the feed, which includes energy from fat as well as from NDF (neutral detergent fiber), NFC (non-fiber carbohydrates) and protein. This allows the company to maintain the balance of energy sources as well as appropriate nutrient to Calorie ratios.
If a product refers to Omega 3 or Omega 6 fatty acids, the actual quantity or % of each fatty acid may also be declared on the tag or on the bag. The ingredient listing will generally identify the oil or oils that may be included in the product.
Top dressing with oil is a common practice, which can be done successfully, when done in moderation with a careful eye on meeting the total nutrient requirements of the horse as well as the energy requirements. Adding too much may result in other nutrient issues.