The evidence behind Synaxis Core
This page sets out the research that informs the Synaxis Core formulation.
Horses convert almost none of the omega-3 in grass into the form their cells actually use.
The evidence falls into three parts: the pathway itself, what changes in blood and tissue, and what changes in the horse.
The mechanism by which EPA and DHA influence inflammatory signalling is characterised largely in human, rodent and canine research. The equine evidence is narrower.
Summary
Horses get omega-3 from grass, almost entirely as ALA. Converting ALA into the long-chain forms the body uses, EPA and DHA, is inefficient in horses, and feeding more ALA does not resolve it.
Fed EPA and DHA reach equine plasma, synovial fluid and lung surfactant over a period of weeks. Dietary omega-3 from plant oils reaches equine skin.
In horses with chronic airway inflammation, adding a DHA-rich algal supplement to a low-dust diet improved cough scores and reduced inflammatory cells in airway fluid beyond what the low-dust diet achieved on its own. That trial set the dose Synaxis Core is built around.
Beyond the airway, equine work has measured joint fluid, insulin sensitivity, the inflammatory response to exercise and the fatty acid composition of skin. In dogs, fed EPA and DHA have improved osteoarthritis and atopic dermatitis.
Why feeding linseed may not be doing what you think
Most omega-3 feeding in horses is based on linseed or linseed oil, which are rich in ALA, the short-chain omega-3 found in plant material. The assumption is that the horse converts ALA into EPA and DHA.
Omega-6 has a poor reputation, and it is only partly deserved. Only one specific omega-6, arachidonic acid, supplies the strongly inflammatory signals. Horses do not eat it, because it sits in animal tissue rather than in plants. They do, however, manufacture it themselves, and how much they manufacture depends on the other fats in the diet.
Both omega-3 and omega-6 families of fat often start as a short version from plants and get built up into the longer ones the body uses to make signals. Omega-3 generally starts as ALA, from grass and linseed. Omega-6 generally starts as linoleic acid, which comes from cereals, soya, sunflower, rice bran and vegetable oils, and makes up a large share of the fat in many hard feeds.
Both families use some of the same pathways to build their longer-chain fats. How much EPA and DHA is ultimately produced depends on the balance of fats entering those pathways, as well as the horse’s limited capacity for conversion. Simply supplying more ALA does not mean that proportionately more EPA and DHA will be made.
So the overall profile of fats the horse receives matters, not just how much omega-3 is in the diet. The overall profile decides how much of the anti-inflammatory and pro-resolving material the horse is able to make.
A University of Florida study supplementing horses with ALA found no meaningful increase in DHA. Circulating EPA can rise on ALA, inefficiently.
Conversion has not been quantified directly in horses. In humans, published estimates for ALA to EPA range from 8 to 20%, and for ALA to DHA from under 0.1% to 9%, varying with sex, genetics and how much linoleic acid is in the diet.
Feeding EPA and DHA directly removes the step altogether.
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. J Anim Sci. 2010;88(1):248-257.
The study that informed our dose
A randomised, placebo-controlled clinical trial at Purdue University College of Veterinary Medicine, published in the Journal of Veterinary Internal Medicine in 2015.
Thirty-five client-owned horses with chronic lower airway inflammatory disease were enrolled and 32 completed. All were moved onto a complete pelleted diet with no hay, the established environmental management for airway disease, then randomly assigned to one of three daily treatments for two months: 30g of an algae-derived omega-3 supplement providing around 1.5g DHA, 60g of the same supplement, or 30g of placebo.
Every group received the low-dust diet, so the differences between them are attributable to the supplement.
| Measure | Supplemented | Placebo |
|---|---|---|
| Cough score | improved 60% | improved 33% |
| Respiratory effort | decreased 48% | decreased 27% |
| Airway neutrophils | fell 23% to 9% | rose 11% to 17% |
The supplement was algae-derived, the same source as Synaxis Core.
Nogradi N, Couetil 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. J Vet Intern Med. 2015;29(1):299-306.
Why dose and time both matter
The Nogradi trial found 1.5g DHA daily sufficient to alter plasma phospholipid composition and produce measurable clinical differences against placebo. Doubling it produced no additional benefit.
Dose alone is not the whole of it. EPA and DHA are incorporated into cell membranes, and that takes weeks.
Twenty horses were fed either 8.82g EPA and 5.35g DHA daily or nothing for 90 days, with blood, joint fluid and lung surfactant sampled at the start and at 30, 60 and 90 days. EPA and DHA appeared in all three, rising in plasma before joint fluid and lung, where the clearest effects came at 60 days.
A separate study fed mares 40g of long-chain omega-3 daily for 91 days and found significant rises in EPA and DHA in synovial fluid as well as serum. Twenty-four horses fed camelina, canola or flaxseed oil for 16 weeks incorporated omega-3 into skin.
Short-term supplementation raises circulating levels without allowing tissue incorporation. That is why Synaxis Core is fed as a 90-day protocol.
What follows sets out what has been measured in each of those tissues.
Christmann U, Hancock CL, Poole CM, et al. 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, et al. Influence of an n-3 long-chain polyunsaturated fatty acid-enriched diet on experimentally induced synovitis in horses. J Anim Physiol Anim Nutr. 2016;100(3):565-577.
Joints
Sixteen horses with arthritis in the knee, fetlock, hock or stifle were divided into two groups for 90 days. Both received the same feed and hay. Eight also received supplements supplying an additional 15g EPA and 19.8g DHA daily, which moved their dietary omega-6 to omega-3 ratio from around 11:1 to around 5:1. Synovial fluid was drawn from an affected joint at day 0, 30, 60 and 90.
The supplemented horses showed a greater fall in synovial fluid white blood cell concentration and in plasma prostaglandin E2, with a trend towards lower plasma fibrinogen. The design changed the ratio and the omega-3 intake together.
At Colorado State University, six mares were fed a diet enriched with 40g of long-chain omega-3 daily for 91 days and six were fed a control diet, with inflammation then brought on in one joint by injection. EPA and DHA rose in the blood and in the joint fluid of the supplemented mares. The markers measured in the joint fluid after the injection were unchanged, and the joint lining of the supplemented mares produced less of an enzyme that breaks down cartilage. The authors concluded that this is worth investigating further.
Separately, horses fed long-chain omega-3 high in DHA raised plasma DHA and may have shown longer trot stride lengths, and dietary microalgae has been assessed against lameness scores and cytokine gene expression in horses.
The clinical work in naturally occurring joint disease has been done in dogs, which develop osteoarthritis as horses do. Thirty-eight dogs with osteoarthritis were randomised to a fish oil diet or a control diet. At 90 days, peak vertical force on the worst-affected limb had improved by 5.6% in the fish oil group against 0.4% in the control group, and 82% of the fish oil dogs improved against 38% of the controls. Seventy-four dogs with radiographically confirmed osteoarthritis were randomised to fish oil at 69mg/kg daily or mineral oil for three months. By day 42, crepitus, pain and joint effusion had improved by around 50% in the fish oil group and were essentially unchanged in the controls.
Manhart DR, Scott BD, Gibbs PG, et al. Markers of inflammation in arthritic horses fed omega-3 fatty acids. Prof Anim Sci. 2009;25:155-160.
Woodward AD, et al. Supplementation of dietary long-chain polyunsaturated omega-3 fatty acids high in DHA increases plasma DHA concentration and may increase trot stride lengths in horses. Equine Comp Ex Physiol. 2007.
Brennan KM, et al. The effect of dietary microalgae on lameness scores and cytokine gene expression in horses. J Anim Sci. 2017.
Roush JK, Cross AR, Renberg WC, et al. Evaluation of the effects of dietary supplementation with fish oil omega-3 fatty acids on weight bearing in dogs with osteoarthritis. J Am Vet Med Assoc. 2010;236(1):67-73.
Mehler SJ, et al. A prospective, randomized, double blind, placebo-controlled evaluation of the effects of eicosapentaenoic acid and docosahexaenoic acid on the clinical signs and erythrocyte membrane polyunsaturated fatty acid concentrations in dogs with osteoarthritis. Prostaglandins Leukot Essent Fatty Acids.
Metabolic health
Managing a metabolic horse usually means limiting fresh grass, by restricting turnout or replacing it with soaked hay. Fresh grass is the dietary source of omega-3, so that management reduces the supply.
In healthy horses given prolonged dexamethasone, which is used experimentally to induce insulin resistance, a DHA-rich microalgae product was associated with lower resting insulin and glucose.
In a pilot study, ten horses with equine metabolic syndrome either received DHA-rich microalgae supplying 16g DHA daily or served as controls for 46 days. Serum triglycerides fell in the treated horses. Over the 46 days the control horses’ insulin response to an oral sugar test rose, while the treated horses’ did not. Fasting insulin did not differ between the groups.
Both studies used the same source as Synaxis Core.
Brennan KM, et al. Effects of a docosahexaenoic acid-rich microalgae nutritional product on insulin sensitivity after prolonged dexamethasone treatment in healthy mature horses. Am J Vet Res. 2015;76(10):889-896.
Elzinga SE, Betancourt A, Stewart JC, et al. Effects of docosahexaenoic acid-rich microalgae supplementation on metabolic and inflammatory parameters in horses with equine metabolic syndrome. J Equine Vet Sci. 2019;83:102811.
The inflammatory response to exercise
Exercise creates inflammation, which is part of how the body adapts to work. How that response is regulated and brought to a close is part of recovery.
Twenty conditioned polo horses were fed a control diet or 10, 20 or 50g of DHA daily for 60 days, then put through lactate threshold tests at the start and at 30 and 60 days. Supplementation altered the inflammatory cytokine response to exercise.
Thirteen Thoroughbreds in early race training were fed 4.3g EPA, 3.5g DHA and 5.3g GLA daily for twelve weeks against a control given ALA and linoleic acid. Twenty-four hours after a standardised exercise test, the supplemented horses had lower IL-8, the signal that calls inflammatory cells to a site, and a trend towards higher IL-10, the signal that damps the response down. The supplement contained GLA, so EPA and DHA were not tested alone.
A 2025 study fed endurance horses a microalgae supplement for 21 days and found no change in heart rate or blood lactate.
In human athletes, systematic reviews report reductions in markers of inflammation and muscle damage after exercise, while improvements in performance have not followed consistently.
Hess T, Braun S, Herkelman K. The effects of various levels of docosahexaenoic acid on inflammatory markers in conditioned horses during lactate threshold tests. J Equine Vet Sci. 2018;72:64-71.
Wesolowski LT, Simons JL, Pagan JD, White-Springer SH. Impacts of exercise and DHA/EPA/GLA supplementation on plasma cytokines in Thoroughbreds. 2022.
Stucchi L, et al. Antioxidant capacity and athletic condition of endurance horses undergoing nutraceutical supplementation. J Equine Vet Sci. 2025.
Skin
Most equine skin work has fed plant oils, which supply ALA rather than EPA and DHA.
Twenty-four horses fed camelina, canola or flaxseed oil for 16 weeks incorporated omega-3 into skin, and the flaxseed group had greater EPA in skin at week 16. Dietary fatty acids change the composition of the skin itself.
Six horses with a positive allergic skin-test response to Culicoides took part in a 42-day placebo-controlled double-blind crossover trial, in which flaxseed significantly reduced the mean area of the skin-test lesion and altered the fatty acid profile of the hair.
A 30-horse, 16-week trial comparing camelina, flaxseed and canola oils found coat colour and quality improved from baseline across all groups, with no differences between the oils in skin barrier function or the inflammatory markers assessed. All three supply ALA alongside linoleic acid in differing proportions, so what separates them is the ratio the horse receives rather than whether omega-3 is present at all.
A 2019 study in 28 horses with Culicoides hypersensitivity applied a cream containing concentrated fish oil to one side of each horse. After four weeks the treated side had significantly improved skin lesions, while itch scores did not change. The cream contained several other ingredients.
In dogs, twenty-nine with atopic dermatitis were randomised for ten weeks to flax oil, to EPA at 50mg/kg and DHA at 35mg/kg, or to mineral oil. Clinical scores improved in both active groups and not in the placebo group. A separate crossover study in sixteen dogs with pruritic skin disease found high-dose fish oil effective against a plant oil control.
O’Neill W, McKee S, Clarke AF. Flaxseed supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. 2002.
Mueller RS, Fieseler KV, Fettman MJ, et al. Effect of omega-3 fatty acids on canine atopic dermatitis. J Small Anim Pract. 2004;45:293-7.
Why these amounts, and why this ratio
Synaxis Core delivers 3.0g DHA and 1.3g EPA per 15ml daily dose.
The airway trial used 1.5g DHA. Core provides 3.0g, which allows a meaningful amount of EPA alongside it, rather than formulating around the DHA dose from the respiratory work alone.
The formulation is DHA-dominant, which reflects the natural composition of Schizochytrium microalgae and the consistent finding in equine research that DHA is the long-chain omega-3 that accumulates in plasma following supplementation.
The carrier is MCT derived from coconut oil, with natural tocopherols for stability. Neither contains active ingredients.