Oil in horse diets
Professor Jo-Anne Murray
PhD, MSc, PgDip, BSc (Hons), BHSII, RNutr, PFHEA University of Glasgow Veterinary School
Oil and oil by-products have been used for many years in equine diets primarily as energy and protein sources, respectively. The proposed benefits of feeding oils to horses include: improved energetic efficiency, improved athletic performance, enhanced body condition, less excitable behaviour, and improved health. Oil by-products, such as oilseed meals, are also valuable feedstuffs for horses due to their high-protein content; in particular soybean meal, which is considered a high-quality protein source due to its high levels of lysine, the first limiting amino acid in the horse.
The use of oil in horse diets
As horses have evolved to exist on a high forage diet, which contains low levels of lipids, fats or oils constitute a minor portion of the diet of forage-fed animals. However, where energy requirements are greater than can be supplied by a forage-only ration, oils are primarily used to increase energy density and/or as a substitute for starchy cereal mixes. Oils are widely available for feeding to horses. Vegetable oils include corn oil, soy oil, sunflower oil, canola (rapeseed) oil and linseed (flax) oil. Fish oils are also used in horse diets, in particular cod liver oil. Most vegetable fats and oils have an energy value of 9 Mcal/kg. Digested fats and oils provide over 2.25 times more utilisable energy than an equal weight of digested carbohydrate or protein and therefore are useful for increasing diet energy density in a bid to increase energy intake and/or decrease the amount of feed required to meet the energy demands of the animal. For example, by utilising fats and oils in the diet there is a reduced requirement for high-levels of supplementary cereal grains, which are known to be detrimental to gut health. Furthermore, pregnant mares in late gestation have a reduced appetite, but increased energy requirements and therefore supplementary fats and oils may be beneficial in this instance. Oil supplementation can also have other potential benefits including; improved energetic efficiency, improved athletic performance, enhanced body condition, less excitable behaviour, and improved health.
Dietary fats (oils) are required to facilitate absorption of fat-soluble vitamins A, D, E and K, and as a source of essential fatty acids (EFAs), such as omega-6 and -3, which the horse’s body can’t produce. Although an EFA requirement for horses is not known, there have been no reports of EFA deficiency in horses. What appears to be more important is the balance of omega-6 and -3; an oversupply of one of these may inhibit the formation of the other family. In humans a ratio of between 2:1 and 3:1 for n-6:n-3 fatty acids is considered optimal. There is currently no reported information on a recommended n-6:n-3 ratio for horses; however, studies have reported a ratio of n-6:n-3 FAs of 6:1 in horses kept at pasture, which is the natural diet for these animals. An overabundance of omega-6 has been associated with some negative effects on cardiovascular health and inflammation in humans and other species. Conversely, omega-3 fatty acids are associated with the opposite, where beneficial effects on cardiovascular, inflammatory, neurological, reproductive and other functions have been reported. However, given that horse diets are naturally low in n-3 they may obtain health benefits from lower n-3 supplementation levels and with a greater n-6:n-3 ratios than that recommended for