DHA for horses: what actually happens when you feed it
Share
Do you take fish oil? If you do, the omega-3 you are taking is mainly EPA and DHA, and the fish did not make those fatty acids. They originated in algae, entered the marine food chain and accumulated in the fish.
Most equine omega-3 supplements work differently, using linseed, which is rich in the shorter-chain omega-3 ALA but contains no DHA. That raises an obvious question: what happens if you skip the conversion step and feed a horse DHA directly?
We know more about feeding DHA to horses than you might think. Researchers have fed long-chain omega-3 to horses and then measured where it goes, including in the blood, joints and lungs.
What is DHA?
DHA, or docosahexaenoic acid, is a long-chain omega-3 fatty acid. Omega-3 is a family of fatty acids, and the three most relevant to feeding horses are ALA, EPA and DHA.
ALA is the shorter-chain form, found abundantly in fresh growing grass and in ingredients such as linseed. EPA and DHA are the longer-chain forms that can be incorporated into cell membranes and used to produce signalling molecules.
Horses can make EPA and DHA from ALA through a series of enzyme pathways, so feeding ALA and feeding DHA directly are quite different nutritional interventions. We look at that distinction in more detail in the difference between ALA and EPA/DHA.
Where does a horse get DHA?
Grass supplies ALA, while DHA originates in the water. Microalgae produce it, and fish and other marine animals consume those algae, directly or indirectly, which is how DHA moves through the marine food chain.
A horse grazing a field takes in plenty of ALA, but for longer-chain omega-3 it depends on converting that ALA through its own metabolic pathways. How much DHA that process actually produces is covered in the conversion step horses depend on, and why it often falls short.
What happens when you feed DHA directly?
The first thing that happens is measurable: the fatty acid composition of the horse begins to change.
Christmann and colleagues followed horses for 90 days while feeding 8.82 g EPA and 5.35 g DHA per day, and they did not just test the blood. They sampled plasma, synovial fluid from the joints and pulmonary surfactant from the lungs, and EPA and DHA increased across all three. Ross-Jones and colleagues found a similar pattern in mares supplemented with long-chain omega-3 for 91 days, with EPA and DHA rising significantly in both serum and synovial fluid.
Feeding ALA has also been tested, and the pattern is different. Hansen and colleagues (2002) fed horses flaxseed oil as a source of ALA, and while plasma ALA and EPA increased, DHA did not. Vineyard and colleagues (2010) likewise found that supplementing ALA changed the fatty acid profile without producing the increase in long-chain EPA and DHA seen when those fatty acids are supplied directly. Hess and colleagues (2012) ran the comparison head to head in mares, feeding matched amounts of omega-3 as either a marine source supplying EPA and DHA or flaxseed meal supplying ALA, and measuring plasma, red blood cells and skeletal muscle: the long-chain fatty acids reached those compartments from the marine source.
Why does that change matter?
Fatty acids are structural components of cell membranes, and they also provide the starting material for chemical signals. The mixture of fatty acids available within a membrane influences which signalling molecules a cell can produce: some participate in initiating and amplifying inflammation, while others regulate that response and help bring it to a close.
EPA and DHA are particularly important here because they provide the raw material for specialised pro-resolving mediators, including resolvins. Resolution is an active biological process, and once the inflammatory response has done its job these signals help bring it to an end while tissue repair and remodelling continue.
Feeding DHA therefore changes the material available to the pathways that control inflammatory signalling.
DHA and horses with breathing problems
The clearest clinical equine work comes from horses with inflammatory airway disease.
Nogradi and colleagues studied 35 horses with recurrent airway obstruction or inflammatory airway disease, of which 32 completed. All of the horses were moved onto a low-dust diet and then randomised to one of three groups: a DHA-rich algal supplement providing 1.5 g DHA per day, the same supplement at double that dose, or placebo.
The low-dust diet helped across the study, and the horses receiving DHA improved further. Cough scores improved by 60% against 33% in the placebo group, and respiratory effort fell by 48% against 27%. There was also a measurable change inside the airways, where neutrophils fell from 23% to 9% in supplemented horses and rose from 11% to 17% in the placebo group.
Plasma DHA rose rapidly and peaked at four weeks, and doubling the supplement dose did not produce a greater clinical effect.
There is more on the relationship between forage, dust and airway inflammation in When horses start coughing.
DHA and joints
Long-chain omega-3 has also been measured inside equine joints. Both Christmann and Ross-Jones found that feeding EPA and DHA changed their concentrations in synovial fluid, which means the fatty acids you put into the feed can alter the fatty acid environment inside the joint.
The equine research has established that they get there. There is also clinical evidence from dogs with naturally occurring osteoarthritis, a useful comparative model, where feeding EPA and DHA has improved weight-bearing and clinical signs in controlled trials.
DHA and metabolic horses
DHA has also been studied in horses with equine metabolic syndrome. Elzinga and colleagues fed 10 affected horses a DHA-rich microalgae providing 16 g DHA per day for 46 days, and circulating DHA increased while serum triglycerides fell.
There was also a difference in insulin response: during the study the control horses showed an increased insulin response to an oral sugar test, while the supplemented horses did not.
How much DHA should you feed a horse?
There is currently no established daily DHA requirement for horses. What we do have are the doses that have actually been used in equine research.
The airway study used 1.5 g DHA per day and the metabolic study used 16 g per day, with the studies looking at incorporation into blood, joints and other tissues sitting between them. That makes the declared amount of DHA per daily serving particularly useful when comparing products.
When choosing a DHA supplement for a horse, four questions tell you considerably more than the words "omega-3" on the front of a tub:
- How many grams of DHA does the horse receive each day?
- How much EPA is supplied alongside it?
- Where do the EPA and DHA come from?
- How is the oil protected from oxygen in storage and during use?
Is algae oil a source of DHA for horses?
Yes, and it is where DHA originates. Microalgae can be grown by fermentation and their oil fed directly, supplying long-chain omega-3 without the fish in the middle of the food chain.
Different algal oils contain different fatty acid profiles, however, so "contains algae" does not tell you how much DHA a horse is actually receiving. The useful numbers are the declared amounts of DHA and EPA per daily serving.
How much DHA is in Synaxis Core?
Synaxis Core contains Schizochytrium algae oil in coconut-derived MCT, stabilised with natural mixed tocopherols. The standard 15 ml daily serving supplies a minimum of:
- 3.0 g DHA
- 1.3 g EPA
That is a minimum of 4.3 g of long-chain EPA and DHA per day.
Synaxis Core was formulated around the amount and form of long-chain omega-3 delivered, rather than the volume of oil in the daily serving.
To see where your horse's diet stands on omega-3, take the Omega-3 Check.
What does the research actually tell us?
When DHA is fed directly to horses, it is absorbed and becomes measurable in the blood and in tissues including synovial fluid and pulmonary surfactant.
That matters because EPA and DHA do more than circulate. They become part of cell membranes and provide the raw material for signalling pathways involved in regulating inflammation.
That gives you something concrete to compare when choosing an omega-3 supplement for a horse: which fatty acids it actually supplies, and how many grams of them reach the horse each day.
References
Christmann U, Hancock CL, Poole CM, Emery AL, Poovey JR, Hagg C, Mattson EA, Scarborough JJ, Christopher JS, Dixon AT, Craney DJ, Wood PL. Dynamics of DHA and EPA supplementation: incorporation into equine plasma, synovial fluid, and surfactant glycerophosphocholines. Metabolomics. 2021;17:41.
Ross-Jones TN, McIlwraith CW, Kisiday JD, Hess TM, Hansen DK, Black J. Influence of an n-3 long-chain polyunsaturated fatty acid-enriched diet on experimentally induced synovitis in horses. Journal of Animal Physiology and Animal Nutrition. 2016;100(3):565–577.
Vineyard KR, Warren LK, Kivipelto J. Effect of dietary omega-3 fatty acid source on plasma and red blood cell membrane composition and immune function in yearling horses. Journal of Animal Science. 2010;88(1):248–257.
Hess TM, Rexford JK, Hansen DK, Harris M, Schauermann N, Ross T, Engle TE, Allen KGD, Mulligan CM. Effects of two different dietary sources of long chain omega-3, highly unsaturated fatty acids on incorporation into the plasma, red blood cell, and skeletal muscle in horses. Journal of Animal Science. 2012;90:3023–3031.
Hansen RA, Savage CJ, Reidlinger K, Traub-Dargatz JL, Ogilvie GK, Mitchell D, Fettman MJ. Effects of dietary flaxseed oil supplementation on equine plasma fatty acid concentrations and whole blood platelet aggregation. Journal of Veterinary Internal Medicine. 2002;16:457–463.
Nogradi N, Couëtil LL, Messick J, Stochelski MA, Burgess JR. Omega-3 fatty acid supplementation provides an additional benefit to a low-dust diet in the management of horses with chronic lower airway inflammatory disease. Journal of Veterinary Internal Medicine. 2015;29(1):299–306.
Roush JK, Cross AR, Renberg WC, Dodd CE, Sixby KA, Fritsch DA, Allen TA, Jewell DE, Richardson DC, Leventhal PS, Hahn KA. Evaluation of the effects of dietary supplementation with fish oil omega-3 fatty acids on weight bearing in dogs with osteoarthritis. Journal of the American Veterinary Medical Association. 2010;236(1):67–73.
Elzinga SE, Betancourt A, Stewart JC, Altman MH, Barker VD, Muholland M, Bailey S, Brennan KM, Adams AA. Effects of docosahexaenoic acid-rich microalgae supplementation on metabolic and inflammatory parameters in horses with equine metabolic syndrome. Journal of Equine Veterinary Science. 2019;83:102811.