Nutrition

Omega-3 for dogs and cats: why EPA matters

Fish oil is the best-researched supplement for arthritis in dogs. Here's what the studies found, why EPA is the part that counts, and how to choose a product.

By The Animal Physio Co 5 min read

A dog and a cat beside the words "Omega-3: why EPA matters"

If your dog has arthritis, someone has probably suggested fish oil. It's one of the few supplements with good research behind it, but only if you choose the right product and give enough of it. The key is a fatty acid called EPA.

Key points

  • Of all the joint supplements studied, omega-3 from marine sources has the strongest evidence for easing arthritis pain in dogs.1,2
  • EPA is the omega-3 most linked to joint benefits. Plant omega-3s from flax, chia or hemp are a poor substitute, especially for cats.3
  • The amount matters, and more isn't always better. Check with your vet, particularly before surgery or if your animal takes other medication.4
  • Compare products by the milligrams of EPA in a dose, not by "mg of fish oil".

The three omega-3s

There are three omega-3 fatty acids you'll see on labels:

  • EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), the long-chain omega-3s found in fish, krill and marine algae.
  • ALA (alpha-linolenic acid), found in plants such as flaxseed, chia and hemp.

Most of the joint research is on EPA and DHA from marine sources.

How EPA helps inflamed joints

The body makes many of its inflammatory signals from an omega-6 fat called arachidonic acid. EPA competes with arachidonic acid for the same enzymes, so when there's more EPA in the body's cells, it produces milder signals instead.5 In one of the trials below, dogs eating a diet rich in fish oil had less arachidonic acid in their blood within six weeks.6 In a lab study of dog cartilage cells, EPA lowered markers of inflammation, while DHA had little effect.7

What the research shows in dogs

  • In a randomised, double-blind trial of 127 dogs across 18 vet practices, dogs fed a food high in fish-oil omega-3s were better at getting up and playing by week six, and walked better by weeks 12 and 24, than dogs on a typical food, according to their owners.6
  • In a trial of 38 dogs that measured how much weight each dog put on its sore leg using a force plate, 82% of dogs on the fish-oil food improved, compared with 38% on the control food.8
  • In a trial of 131 dogs at 33 vet hospitals, dogs on a fish-oil-enriched food were able to have their anti-inflammatory painkiller (carprofen) reduced faster than dogs on a control food.9
  • Two systematic reviews, ten years apart, both found omega-3 to be the best-supported nutritional option for arthritis in dogs.1,2

Veterinary guidelines agree. The 2022 AAHA pain-management guidelines list omega-3 fatty acids among the first-line, non-drug treatments for long-term pain in dogs and cats,18 and Canadian consensus guidelines on arthritis in dogs include omega-3 (EPA and DHA) in their core recommendations at every stage.19

Most of these trials tested complete therapeutic diets rich in fish oil rather than a supplement on its own. Either way, omega-3 works best alongside your vet's pain relief, weight control and exercise.

What about cats?

Arthritis is far more common in cats than most owners realise. In a study of 100 cats aged six or older, 61% had arthritis on X-rays, and it was linked to less moving about and grooming, and to toileting outside the litter tray.10 Cats hide stiffness by sleeping more and jumping less, so it's easily missed.

The research on omega-3 in cats is smaller but encouraging:

  • In a crossover trial of 16 arthritic cats, owners reported less stiffness and higher jumping while their cats were on fish oil compared with corn oil.11
  • In a trial of 40 cats, a diet rich in EPA and DHA (which also contained green-lipped mussel and glucosamine-chondroitin) increased the cats' measured activity.12

There's no established safe upper limit for cats,3 so let your vet set the dose.

Why plant omega-3 isn't the same

To help joints in the way described above, ALA has to be converted into EPA and DHA. Dogs do this poorly, and in cats conversion is virtually zero because they lack enough of the enzyme involved.3 In one study, dogs fed a flaxseed diet had higher EPA in their blood but no detectable DHA.13 Look for a marine source instead: fish oil, krill oil or algal oil.

How much is enough?

Published guidance puts arthritis at the top of the therapeutic range for EPA and DHA.14 There's also a safe upper limit for dogs, set by the US National Research Council at 2.8 g of EPA and DHA per 1,000 kcal the dog eats.3 That works out at roughly 2,080 mg a day for a 10 kg dog.15 For larger dogs, the top of the therapeutic range can exceed that limit.

Because the right amount depends on your animal's weight, diet, other medication and health, ask your vet or physiotherapist to work out a dose rather than following the tub alone.

Side effects and cautions

Fish oil is generally well tolerated, but a review of the research lists possible problems, which are more likely at higher doses:4

  • Stomach upset and loose stools
  • Weight gain, because oil is high in calories
  • Changes in blood clotting and slower wound healing, so tell your vet before any surgery
  • Oxidation of the oil, which is why good products add an antioxidant such as vitamin E
  • Interactions with other medicines

Speak to your vet first if your animal is on other medication, has a bleeding disorder or diabetes, or is due for an operation.

How to choose a product

  1. Look for the mg of EPA and DHA per dose. "1,000 mg fish oil" does not mean 1,000 mg of omega-3.
  2. Choose a marine source: fish, krill or algae, not flax or chia.
  3. In South Africa, check the label for a registration number. Pet foods and feeds show "Reg. No. V…, Act 36 of 1947",16 and it's illegal to sell one that isn't registered.17
  4. Look for an added antioxidant such as vitamin E. Keep the oil cool and closed, and throw it away if it smells rancid.
  5. Use a product made for your species, dosed for your animal's weight.

Where physiotherapy fits

Omega-3 can take the edge off joint pain, but muscles are what keep arthritic joints stable and moving. At The Animal Physio Co we combine a home exercise programme, hands-on therapy and treatments such as laser with your vet's plan for pain relief and weight. If your dog or cat is slowing down, book an assessment and we'll come to you.

References

  1. Barbeau-Grégoire M, Otis C, Cournoyer A, et al. A 2022 systematic review and meta-analysis of enriched therapeutic diets and nutraceuticals in canine and feline osteoarthritis. International Journal of Molecular Sciences. 2022;23(18):10384.
  2. Vandeweerd JM, Coisnon C, Clegg P, et al. Systematic review of efficacy of nutraceuticals to alleviate clinical signs of osteoarthritis. Journal of Veterinary Internal Medicine. 2012;26(3):448–456.
  3. Lenox CE. Role of dietary fatty acids in dogs and cats. Today's Veterinary Practice. 2016. Includes the National Research Council (2006) safe upper limit.
  4. Lenox CE, Bauer JE. Potential adverse effects of omega-3 fatty acids in dogs and cats. Journal of Veterinary Internal Medicine. 2013;27(2):217–226.
  5. Bauer JE. Therapeutic use of fish oils in companion animals. Journal of the American Veterinary Medical Association. 2011;239(11):1441–1451.
  6. Roush JK, Dodd CE, Fritsch DA, et al. Multicenter veterinary practice assessment of the effects of omega-3 fatty acids on osteoarthritis in dogs. Journal of the American Veterinary Medical Association. 2010;236(1):59–66.
  7. Adler N, Schoeniger A, Fuhrmann H. Polyunsaturated fatty acids influence inflammatory markers in a cellular model for canine osteoarthritis. Journal of Animal Physiology and Animal Nutrition. 2018;102(2):e623–e632.
  8. 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. Journal of the American Veterinary Medical Association. 2010;236(1):67–73.
  9. Fritsch DA, Allen TA, Dodd CE, et al. A multicenter study of the effect of dietary supplementation with fish oil omega-3 fatty acids on carprofen dosage in dogs with osteoarthritis. Journal of the American Veterinary Medical Association. 2010;236(5):535–539.
  10. Slingerland LI, Hazewinkel HA, Meij BP, et al. Cross-sectional study of the prevalence and clinical features of osteoarthritis in 100 cats. The Veterinary Journal. 2011;187(3):304–309.
  11. Corbee RJ, Barnier MM, van de Lest CH, et al. The effect of dietary long-chain omega-3 fatty acid supplementation on owner's perception of behaviour and locomotion in cats with naturally occurring osteoarthritis. Journal of Animal Physiology and Animal Nutrition. 2013;97(5):846–853.
  12. Lascelles BD, DePuy V, Thomson A, et al. Evaluation of a therapeutic diet for feline degenerative joint disease. Journal of Veterinary Internal Medicine. 2010;24(3):487–495.
  13. Dunbar BL, Bigley KE, Bauer JE. Early and sustained enrichment of serum n-3 long chain polyunsaturated fatty acids in dogs fed a flaxseed supplemented diet. Lipids. 2010;45(1):1–10.
  14. Raditic D, Gaylord L. Fish oil dosing in pet diets and supplements. Today's Veterinary Practice. Updated 2024.
  15. Garcia JL. Journal scan: omega-3 fatty acids: how much is too much? dvm360. 2013.
  16. Department of Agriculture. Regulations relating to farm feeds (R.1087 of 2006), regulation 22.
  17. Fertilizers, Farm Feeds, Agricultural Remedies and Stock Remedies Act 36 of 1947, section 7.
  18. Gruen ME, Lascelles BDX, Colleran E, et al. 2022 AAHA pain management guidelines for dogs and cats. Journal of the American Animal Hospital Association. 2022;58(2):55–76.
  19. Mosley C, Edwards T, Romano L, et al. Proposed Canadian consensus guidelines on osteoarthritis treatment based on OA-COAST stages 1–4. Frontiers in Veterinary Science. 2022;9:830098.

This article is general information, not veterinary advice. Speak to your vet before starting any supplement or treatment, and ask a qualified animal physiotherapist to assess your animal individually.