The Positive and Negative Effects of Oil in Equine Nutrition

Oil is a regular addition to modern racing diets, either by feeding a high oil-containing racing feed or through extra addition of liquid vegetable oil. Research over the years has shown that oil is palatable to horses and digested very well, and that there is little difference in digestibility between the main types of vegetable-based oils used. Oil that is integral to feed ingredients, such as that found in rice bran, linseed, naked oats, soya, etc., may have a marginally lower digestibility, as this will depend on how digestible the encapsulating matrix is to the horse. However, in the main both free oil and integral oil is well tolerated and digested in horses.         In a natural environment, horses can easily consume between 2-3% of their body weight as dry matter from pasture. Oil has always been a natural part of the horse's diet, as grass contains about 2-3%, which may seem low but can provide the equivalent of 200-400mls of oil per day. Other forages, such as hay, haylage, and chaff, will also contain oil at a similar level on a dry matter basis.         Horses can tolerate up to 20-25% of their total energy intake coming from oil, and this has been exploited successfully to help manage rhabdomyolysis related to exercise (exertional rhabdomyolysis syndrome, or ERS) or aberrant carbohydrate metabolism (Polysaccharide storage myopathy). [See Diet Example 1.]         However, the level of oil that individuals can tolerate in their diet will vary and is likely to be dependent on variations in enzymatic lipase activity and speed of passage through the small intestine.  It quickly becomes apparent if you have too much oil in the diet of a particular horse, as their droppings tend to become looser and they often develop a fairly unpleasant smell, which can be a sign to pull back on the oil inclusion.        There are many advantages to feeding additional oil within a racing ration, some of which relate to its extremely high energy content compared with carbohydrate.  When directly compared with oats on a weight-for-weight basis, oil delivers 70% more energy.  Other potential advantages depend on the chemical makeup of the oil, in terms of its constituent fatty acids. Oils are made up principally of triglycerides, which consist of three free fatty acids of varying types bound to a single glycerol. The relative proportions of the different free fatty acids contribute to the physical characteristics of an oil, for example, whether they are liquids or solids at room temperature and how they behave biochemically in the body. There are many different types of fatty acids, characterised by the carbon chain length of their core structure and the number and position of double bonds within this chain. Like amino acids, there are also dietary essential fatty acids, principally linoleic acid and linolenic acid, which must be provided, as they cannot be synthesised.  Fatty acids are grouped structurally into distinct families which behave in a similar fashion, which include the omega-3, omega-6, and omega-9 fatty acids. There are also medium chain fatty acids which are a further group of structurally different saturated fatty acids (with no double bonds).                 Diet Example 1 – High-oil ration for horse at risk of exertional rhabdomyolysis           % Oil    Oil Contribution    Hay fed at 8kg    2%    430g    Alfalfa fed at 2kg    2.5%    50g    8% oil racing feed fed at 6kg    10%    480g    Micronised linseed fed at 500g    40%    200g    Total       1160g       Total energy intake DE from diet approximately 162 MJ per day    Total energy intake from oil approximately 40 MJ/day    Contribution of oil to total energy intake of oil 25%    The racing feed is likely to deliver mostly omega-6 fatty acids, whereas the hay, alfalfa, and linseed will offer balancing omega-3 fatty acids.        Family Rivalry – The Omegas    The essential fatty acid linoleic acid belongs to the omega-6 family, while alpha linolenic acid belongs to the rival family of omega-3.  These essential fatty acids must be provided in the diet, as they cannot be synthesised by the body.  Each is the parent compound for an extended family of longer chain bioactive fatty acids, which can eventually be used to form hormone-like substances called eicosanoids. The eicosanoids, which include prostoglandins, prostacycline, thromboxanes, and leukotriens, can be derived from omega-6 or omega-3 and influence many physiological processes, including the immune response, inflammation, and blood coagulation. The formation of these eicosanoids from their omega-6 or omega-3 parents depends on how much is present in the body, as they are formed through competing common enzymatic pathways and this in turn is influenced by diet. Active competition between these two families of fatty acids ultimately influences their relative effects on these important body processes, and there is a balance to be struck.  There is little information on where that balance lies in horses, but suffice to say that most high-oil containing ingredients found in a racehorse’s concentrate diet are rich in the omega-6 fatty acids with a predominance of linoleic acid, with much less omega-3 fatty acids being present.         Pasture is a rich source of the omega-3 fatty acid alpha linolenic acid. In fact, data suggests that alpha linolenic acid makes up a large proportion of the oil in pasture and could be as high 50-70%. This has been highlighted by advocates of the organic movement and ‘clean eating’ lobby in human nutrition, who suggest that this higher intake of omega-3 by grass-fed cows transfers health benefits to both their meat and milk, compared to grain-fed animals. The benefits of a diet with a suitable omega-3:omega-6 ratio is more understood in human nutrition than in horses, with research suggesting health benefits to the respiratory system, immunity, mental health, and skeletal integrity, presumably being brought about by balancing the pro-inflammatory and anti-inflammatory effects of these two fatty acid families. I find it very interesting how nature often provides what seems to work, and by moving horses in training farther away from their natural diet, we have inadvertently shifted towards a diet that is richer in omega-6 fatty acids and potentially more pro-inflammatory. It is important to remember that inflammation is an important part of the healing process and so it should not be regarded as a complete negative.  Whilst the omega-3 fatty acid content of hay and haylage is lower than pasture, it still delivers a significant level of omega-3 fatty acid in the form of linolenic acid, helping to offset the omega-6 fatty acids which predominate within the concentrate feed. This yet again highlights the need for a high level of forage/access to pasture to be maintained for horses in training.          The use of linseed meal has recently increased both as an ingredient in proprietary horse feed and as a standalone supplement for top dressing.  As can be seen from Table 1, linseed has one of the highest omega-3: omega-6 ratios. Equally, rapeseed oil or canola oil has an increased omega-3 content compared to corn or soya oil.          Oily fish    Although alpha linolenic acid is a precursor of the longer chain, more bioactive omega-3s, eicosapentanoic acid (EPA), and docosahexanoic acid (DHA), the efficiency of conversion is quite low, estimated to be only 5-10% in other species. Whilst the contribution of alpha linolenic acid may have some benefit, other 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 or salmon oil – as well as green-lipped mussel have been used in small amounts as a rich source of DHA and EPA. However, the fishy smell can be off-putting and there is the whole moral question of whether herbivores should be eating fish.   Plant sources of DHA in the form of algae (similar in makeup to what fish eat in their diet) are now more commonly seen in equine products, primarily supplements.         There is little data in horses on the optimum ratio of omega-3 to omega-6 fatty acids. In humans it is suggested that a ratio nearer to 1:1 is healthier, although a Western diet can be 1:10-15. The ratio of omega-3 to omega-6 seems to be as important as the absolute level of omega-3 present in the diet.  This may also depend on the type of omega-3 delivered, given the inefficient conversion of linolenic acid to DHA and EPA.         There are a few studies that have looked at the efficacy of omega-3 fatty acids in horses.  A preliminary study using ponies with sweet itch suggested a beneficial effect of linseed / flax on this inflammatory skin condition when fed at a level equivalent to 500g for a 500kg horse daily. Encouraging results have also been reported for the effect of supplementation with a combination of EPA and DHA on arthritic horses with a significantly lower concentration of white blood cells in synovial fluid being present and lower plasma levels of PGE2 (an inflammatory prostaglandin) in horses supplemented with a pelleted product providing 15g of EPA and 20g of DHA for 90 days, compared to a non-supplemented control group. This follows on from work carried out that suggests an increase in stride length in horses supplemented with EPA and DHA.       In humans, there is also some evidence to support a protective role for omega-3 fatty acids in asthma, a condition that is not unlike recurrent airway obstruction (RAO) in horses, although the results are not indisputable. A supplementation study with omega-3 fatty acids in horses, however, did not significantly alter clinical indicators of pulmonary function, although the white blood cell counts in epithelial lung-lining fluid were reduced in the omega-3 supplemented horses. This may suggest an effect of supplementation on pulmonary inflammation.       A supplement containing both omega-3 fatty acids and additional vitamins perhaps unsurprisingly delivered a change in the omega-3 to omega-6 ratio in plasma, but more significantly, it delayed the characteristic fall in red blood cell membrane fluidity seen during exercise because of splenic contraction and increased viscosity, which is important to maintain unfettered blood flow and reduce pressure in small blood vessels.          Medium-chain fatty acids    Oils such as coconut and palm oil contain a high proportion of medium-chain fatty acids (C6 – C10). Copra is a feed ingredient that is now more widely available for horses, and it is made from the white parts or flesh of the coconut.  Characteristically, it has a low non-structural carbohydrate content (NSC) and is particularly low in starch, making it an attractive feed ingredient. It typically has an oil content of about 8-10% and this oil is saturated, making it less likely to go rancid during storage.       Medium-chain fatty acids are absorbed from the intestines more quickly and with less breakdown and re-assimilation needed compared to long-chain fatty acids. Medium-chain fatty acids are interesting as a fuel source, as they don’t depend on L-carnitine for their transport into the mitochondria, which is the powerhouse of the cell. It has been proposed that this simplified absorption from the gut and transport within muscle cells may offer a potential advantage for performance, and early research suggested this may be the case. However, follow-up studies failed to reproduce these results, so any beneficial effect on performance remains controversial.         Oil production.    There are a number methods of production, including solvent extraction and cold pressing, used to deliver vegetable-based oils. The former involves the use of solvents such as hexane and a variety of intensive processing to extract the maximum amount of oil from the oilseed to produce an oil that is light coloured, not highly flavoured, and can withstand oxidation. In contrast, cold-pressed oils undergo a much less intensive low-temperature process and yield less oil, but may retain more of the minor nutrients, contain less trans fatty acids, and retain more of the natural flavour. There is obviously a cost implication of the different methods of processing and there has been no work done to date to suggest any benefit or disadvantage to either type for horses thus far.       Due to the high propensity for oxidation of oils, particularly those with a high polyunsaturated nature, they will usually contain natural antioxidants in the form of vitamin E-like substances, which may benefit the horse.  Equally though, the current advice when adding oil the diet is to add a further 100iu of vitamin E for every 100ml of oil added.       In summary, a racing diet supplemented with oil has many nutritional and practical advantages. Oil offers an energy-dense feed ingredient that is devoid of simple carbohydrate and starch. Whilst there is currently insufficient information on the requirements of horses for omega-3 fatty acids and the optimum ratio compared to omega-6, there is a balance to be struck. The predominance of the omega-3 fatty acid alpha linolenic acid in pasture and forages offers further rationale for maintaining a high-forage-to-concentrate ratio in all racing diets.  

Published in European Trainer, January - March 2018, issue 60.

Oil is a regular addition to modern racing diets, either by feeding a high oil-containing racing feed or through extra addition of liquid vegetable oil. Research over the years has shown that oil is palatable to horses and digested very well, and that there is little difference in digestibility between the main types of vegetable-based oils used.

Oil that is integral to feed ingredients, such as that found in rice bran, linseed, naked oats, soya, etc., may have a marginally lower digestibility, as this will depend on how digestible the encapsulating matrix is to the horse. However, in the main both free oil and integral oil is well tolerated and digested in horses.  

In a natural environment, horses can easily consume between 2-3% of their body weight as dry matter from pasture. Oil has always been a natural part of the horse's diet, as grass contains about 2-3%, which may seem low but can provide the equivalent of 200-400mls of oil per day. Other forages, such as hay, haylage, and chaff, will also contain oil at a similar level on a dry matter basis.  

Horses can tolerate up to 20-25% of their total energy intake coming from oil, and this has been exploited successfully....

To read more - subscribe now!

Buy this issue online here

Gallery

Trainer Profile: Colin Tizzard

Back to School: Dressage as a Training Tool

0