Oiling the Wheels - using oil as a supplement in the diet of racehorses

Historically, oil has not featured highly in the diets of horses in training, or indeed those of other horses. 
The natural oil content of pasture and other forages is quite low at between 2-3% on a dry matter basis, yet despite this, horses digest oil extremely well. Oil added to the racehorses’ diet is tolerated well, with no major palatability problems having been reported.

There are many advantages to feeding an oil supplemented diet to horses in training. For feed manufacturers, the addition of increasing amounts of oil in a feed formulation allows the addition of energy or ‘calories,’ without any contribution towards the starch and protein content of the feed. This means that lower starch feeds can be produced, whilst maintaining the total energy content of the feed. This type of diet can help prevent the digestive system from being overwhelmed by the presence of starch in the diet. Additionally, beneficial effects of this type of diet on behaviour have also been reported and horses that are prone to tying up may also gain.

Oil supplementation can also potentially bring other beneficial effects e.g. on coat condition and on respiratory health or mobility and performance. However these additional desirable effects are likely to depend not only on the quantity of oil within the daily ration, but also on the nature of the oil included.


The energy or calorie content of oil is higher than any other ingredient commonly used in the manufacture of racing feeds.

In a direct comparison with oats, vegetable oil such as corn oil provides about 70% more energy for a given weight. From a trainer’s perspective, top dressing oil onto an existing ration allows an increase in the energy density of the feed i.e. more calories for the same volume of feed. This is particularly useful for fussy feeders helping to keep their meal sizes relatively small.
Ingredient Energy (MJ/kg)
Corn Oil 38 
Oats 12.5 
Racing Mix 13
 Hay 7.5

Oil is usually added into the diet in oz or ml rather than in kilograms. So for a more practical comparison, a coffee mug of oil, which is equivalent to about 250ml (225g), would provide about 9 MJ of energy, which is equivalent to about ¾ of a flat scoop of oats (750g).

There are many types of oil besides corn and soya that have been fed to horses over the years. Vegetable oils derived from rapeseed or canola, sunflower, safflower, coconut and even peanut have been previously fed. Fish oils such as tuna oil, salmon oil and cod liver oil have also been used. Cod liver oil should, however, be used sparingly due to the high fat soluble vitamin content.

Other high oil containing ingredients that are commonly used in racing feeds, or in some cases to top-dress racing diets, include rice bran, linseed meal, full fat soya and naked oats.

Whilst the oil content of all of these ingredients is relatively high, the starch content varies quite significantly. In terms of oil delivery and starch content, linseed meal would clearly be a good choice for oil supplementation where a low starch containing diet was desired.
Ingredient % Oil Content % Starch Content
Ricebran 16-20 15-27 
Linseed Meal 37 5.5 
Full Fat Soya 20 4.5 
Naked Oats 10 53


There has been some suggestion in the scientific literature in recent years that feeding a ration that is high in oil and fibre and low in starch can have a beneficial effect on behaviour, in terms of reducing excitability.  Studies on Thoroughbreds with recurrent exertional rhabdomyolysis (RER) reported decreased excitability and nervousness, as well as lower resting heart rates, when they were fed a low starch high oil containing diet, compared with an isocaloric diet that was low in oil and high in starch. This effect, however, is likely to have been mostly due to the reduction in starch intake from cereal, rather than the oil content per se. The use of increased amounts of oil in the diet does, however, facilitate the reduction in starch content without leaving an ‘energy gap.’   


More recently, stress has been implicated as a trigger for RER in susceptible horses and so the potentially beneficial effects of oil supplemented diets that are also low in starch and high in fibre have been extolled. Accordingly, lower plasma concentrations of creatine kinase (CK) following a standard exercise test have been reported in response to such diets, in comparison to traditional racing type diets that are high in starch and low in fibre and oil. Specialists on RER have successfully advocated the use of such diets for horses in training that are at risk from RER. In addition, there is a strong argument for the use of such diets during pre-training and the early part of actual training. Significant oil supplementation during full training, if the starch content of the diet is also drastically reduced, is more controversial due to the metabolic effects that can be induced and so the potential effect on subsequent exercise performance.


Putting this section into context, the metabolic adaptations to oil supplementation have been reported to occur when relatively large quantities of oil are fed, typically where near to 20% of the total dietary energy intake is provided by oil. For a cube or a mix fed at, for example 6kg per day, this would require a 10% declaration of oil for that feed. For comparison most racing feeds would contain oil at the level of inclusion of 5 - 8.5%.

A high level of oil supplementation has been reported latterly to decrease resting muscle glycogen concentration and improve the use of fat as a fuel source during low and moderate intensity exercise (trotting through to slow cantering) through metabolic adaptation at the muscle level. This offers the possibility of sparing muscle glycogen stores during low intensity exercise training, but equally may impede muscle glycogen replenishment following hard work or racing, which may disadvantage (see European Trainer Issue 19 Racing Power - Supporting Muscular Effort through Nutrition).

The effect of oil supplementation on high intensity exercise performance such as racing is very controversial. Some studies show little or no effect, whilst others have shown a beneficial effect. As a result the scientific community are divided and so the jury is still very much out in this respect.


Dietary oil also provides a source of what are termed essential fatty acids, namely linoleic acid, which belongs to the omega 6 family of fatty acids and α-linolenic acid, which belongs to the rival family the omega 3’s. Most ingredients found in a racehorses’ diet are rich in the omega 6 type of fatty acid with much less omega 3 fatty acid present.

The role for dietary omega-3 fatty acids which has been proposed in maintaining joint and skin health, and in supporting immune function, fertility and respiratory health, makes them an attractive nutraceutical ingredient for racehorses. The use of linseed meal has recently increased in proprietary horse feed and supplements. However, although α-linolenic acid is a precursor of the longer chain more bioactive omega 3’s, eicosapentanoic acid (EPA) and docosahexanoic acid (DHA), the efficiency of conversion is quite low.

Therefore nutraceutical ingredients that provide a more concentrated source of either or both EPA and DHA are becoming more widely used. Ingredients such as micro-encapsulated and deodorised fish oils e.g. tuna oil, as well as green lipped mussel, and more recently plant sources of DHA in the form of algae are now more commonly seen in equine products, primarily supplements.

Few studies into the efficacy of omega-3 fatty acids have, however, been published in horses. In a preliminary study using ponies with sweet itch, a beneficial effect of linseed on inflammatory skin conditions was proposed. Encouraging results have also been reported for the effect of supplementation with a combination of EPA and DHA on arthritic horses.

In humans there is some evidence to support a protective role for omega-3 fatty acids in human asthma, a condition that is not unlike recurrent airway obstruction (RAO) in horses, but the results are not indisputable.  A recent supplementation study with omega 3 fatty acids in horses, however, did not significantly alter clinical indicators of pulmonary function, although the leukocyte counts in epithelial lung lining fluid were reduced in the omega-3 supplemented horses. This may suggest an effect of supplementation on pulmonary inflammation.


The answer to this question is not straightforward as if you are intending to top dress oil onto feeds, the quantity required will largely depend on how much is present in the basal diet already.  Certainly, where the oil is being used to increase the energy density of the diet and reduce the inclusion of starch rich ingredients, a level of 250-300ml per day to replace a kilo of oats or other racing feed would not be inappropriate, where the basal diet contained a low level of oil. For horses that struggle to maintain condition, addition of 100-150mls of oil daily into the existing ration is likely to help.

One should always remember, however, that oil does not provide any protein or vitamins and minerals and so must be fed in conjunction with a balanced diet, particularly with respect to antioxidant vitamins such as vitamin E. Oil should always be introduced to the diet slowly and the daily amount spread over several meals. In addition, any adverse affect on dropping consistency may be a warning that the level of oil in the total diet is too high and the level should be reduced.

As far as the neutraceutical omega 3 fatty acids are concerned, we know much less about the quantities required, but hopefully research will continue in this area to investigate their potentially beneficial effects.

Pelvic asymmetry in racehorses - increased risk of injury?

Derby Starters - where do they go from there?