Omega-3 and horses' joints: what the research has measured

Joints are one of the most common reasons owners start looking at omega-3 for horses. Researchers have studied horses that already had arthritis, measured whether EPA and DHA reach the fluid inside the joint, and looked at what happens when joint inflammation is deliberately brought on.

What happens in a joint

A joint is where two bones meet. Cartilage covers the ends of the bones to give a smooth surface, and a thick liquid called joint fluid, or synovial fluid, keeps the joint moving freely.

When a joint is irritated or damaged, immune cells arrive in the joint fluid and the tissue produces inflammatory signals, one of which is prostaglandin E2. That reaction is how the body deals with injury, and in an arthritic joint it tends to keep going.

The study in arthritic horses

Manhart and colleagues (2009) studied 16 mature horses with arthritis in the knee, fetlock, hock or stifle. The horses were matched by how bad the arthritis was, which joints were affected and their age, then split into two groups.

All 16 got the same feed and hay. Eight also got supplements supplying EPA and DHA every day. Joint fluid was taken from an affected joint at the start and at 30, 60 and 90 days.

In the supplemented horses, immune cells in the joint fluid fell further than in the controls, and so did prostaglandin E2 in the blood. Fibrinogen, another blood marker that rises with inflammation, was lower in them too. Seven horses were also stood on a force plate to measure the weight going through the sore leg, which did not differ between the groups.

Do EPA and DHA get into the joint?

Christmann and colleagues (2021) fed 20 horses EPA and DHA daily for 90 days, or nothing extra, sampling blood, joint fluid and the fluid lining the lungs at the start and at 30, 60 and 90 days. EPA and DHA rose in all three, and the amount in the joint fluid peaked at 60 days. What a horse eats changes the fats inside its joints, over weeks rather than days.

Ross-Jones and colleagues (2016) fed 12 mares either a normal diet or one enriched with long-chain omega-3 for 91 days, then brought on inflammation in one joint by injection. EPA and DHA rose in the blood and joint fluid of the supplemented mares. Every horse reacted to the injection, and the diet did not change the inflammatory markers in the joint fluid afterwards. What differed was the joint lining, which in the supplemented mares produced less of an enzyme that breaks down cartilage. The researchers said it is worth investigating further.

What the dogs show

Dogs get arthritis naturally as horses do, the studies are bigger, and they have measured something the horse studies have not: whether the animal moves better.

Roush and colleagues (2010) split 38 arthritic dogs between a food containing fish oil and a control food, measuring the weight each dog put through its worst leg at the start and at 45 and 90 days. Over 90 days that weight rose by 5.6% in the fish-oil dogs, a real difference, and by 0.4% in the controls, which was not. Weight-bearing improved in 82% of the fish-oil dogs and 38% of the controls.

What it adds up to

Three things have been measured in horses. EPA and DHA fed in the diet reach the fluid inside the joint, and take weeks to build up there. In horses that already had arthritis, the ones getting EPA and DHA had fewer immune cells in that fluid and lower inflammatory markers in their blood. In horses whose joints were deliberately inflamed, the joint lining produced less of the enzyme that breaks down cartilage.

What the horse studies have not measured is movement. Manhart's force plate went on only seven horses and showed nothing, so that question is still open in horses and further research is necessary. The dogs are as close as the evidence currently gets, and there the animals did put more weight through the sore leg.

The other half of the picture is what a horse is getting already. Grass supplies omega-3 as ALA, the short-chain form, and horses turn very little of it into EPA and DHA. A horse on hay, or with its grazing cut back, takes in less omega-3 than one out at grass, and in either case it is the short-chain form. So the fatty acids the joint studies were measuring are the ones a horse is least likely to have much of.

Feeding EPA and DHA to a horse

The joint studies ran for around 90 days, with the amount in the joint fluid still climbing at 60. What matters in a supplement is which fatty acids it supplies, how much of them the horse gets each day, and how long it is fed for.

Synaxis Core is an algae oil fed at 15 ml a day, giving 3.0 g DHA and 1.3 g EPA. It supplies EPA and DHA straight, without the horse having to make them from ALA, and it is fed as a 90-day protocol to match the period the research used.

EPA and DHA belong in a holistic approach to joint health, used alongside appropriate veterinary care, exercise, management and nutrition.

To see where your horse's diet stands on omega-3, take the Omega-3 Check.

References

Manhart DR, Scott BD, Gibbs PG, Coverdale JA, Eller EM, Honnas CM, Hood DM (2009). Markers of inflammation in arthritic horses fed omega-3 fatty acids. The Professional Animal Scientist 25:155-160.

Christmann U, Hancock CL, Poole CM, et al. (2021). Dynamics of DHA and EPA supplementation: incorporation into equine plasma, synovial fluid, and surfactant glycerophosphocholines. Metabolomics 17:41.

Ross-Jones TN, McIlwraith CW, Kisiday JD, Hess TM, Hansen DK, Black J (2016). 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 100(3):565-577.

Roush JK, Cross AR, Renberg WC, et al. (2010). 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 236(1):67-73.