Short answer: EPA (eicosapentaenoic acid, 20:5n-3) is a long-chain omega-3 polyunsaturated fatty acid synthesized in marine microalgae (principally Nannochloropsis, Phaeodactylum, Pavlova) and concentrated up the marine food chain into the body fats of cold-water fish (salmon, herring, sardine, anchovy, menhaden) per Bauer 2011 (J Am Vet Med Assoc) canine essential fatty acid review and ACVIM 2018 consensus statement on cardiovascular omega-3 supplementation. Per Mehler 2016 (Prostaglandins Leukot Essent Fatty Acids), EPA serves as the precursor for the series-3 prostaglandins (PGE3, PGI3), series-5 leukotrienes (LTB5), and E-series resolvins (RvE1, RvE2, RvE3) which collectively exert anti-inflammatory effects distinct from the pro-inflammatory series-2 eicosanoids derived from omega-6 arachidonic acid. Per AAFCO 2024 Official Publication, canine growth and reproduction formulas require a minimum 0.05 percent combined EPA+DHA on a dry-matter basis; canine adult maintenance has no required minimum. Per Roush 2010 (J Am Vet Med Assoc) double-blind randomized controlled trial in 127 dogs with osteoarthritis, the therapeutic combined EPA+DHA dose for clinically meaningful symptom reduction is 40–80 mg per kg body weight per day. The KibbleIQ rubric treats EPA as a positive ingredient at meaningful dose: formulations with fish oil, salmon oil, krill oil, or algal-oil supplementation listed in the top 15 ingredients earn positive credit; trace-amount fish-oil inclusion below the omega-3 nutritional minimum earns no credit.

Molecular structure and biosynthesis pathway

Per Bauer 2007 (J Am Vet Med Assoc) canine essential fatty acid review and Calder 2017 (Biochem Soc Trans) omega-3 metabolism review, EPA is a 20-carbon polyunsaturated fatty acid with five cis-double bonds at positions 5, 8, 11, 14, and 17 from the methyl terminus — the IUPAC shorthand 20:5n-3 (also written 20:5ω-3). The n-3 designation specifies that the first double bond from the methyl terminus is at the third carbon, which defines membership in the omega-3 family along with alpha-linolenic acid (18:3n-3), DPA (22:5n-3), and DHA (22:6n-3).

Per Calder 2017 and Bauer 2011 (J Am Vet Med Assoc), mammals (including dogs and cats) cannot synthesize alpha-linolenic acid (ALA, 18:3n-3) de novo because they lack the n-3 desaturase enzyme; ALA must therefore be obtained from dietary plant oils (flaxseed, chia, hempseed, perilla, canola). ALA can be elongated and desaturated to EPA via the desaturase-elongase pathway (Δ6-desaturase, elongase, Δ5-desaturase), but the canine conversion efficiency is approximately 5–15 percent, and the feline conversion efficiency is essentially nil because cats have minimal Δ6-desaturase activity per Pawlosky 1994 (J Nutr) feline fatty acid metabolism work. The practical pet food implication is that dietary EPA must be supplied as pre-formed EPA (from marine sources or direct algal-oil supplementation) rather than relying on plant-source ALA conversion. The plant-source ALA cluster overlaps with our flaxseed oil explainer, chia oil explainer, hempseed oil explainer, perilla oil explainer, and canola oil explainer.

Pet food source ingredients and concentration ranges

Per WSAVA 2018 Global Nutrition Guidelines and AAFCO 2024 Official Publication ingredient definitions, pet food supplies pre-formed EPA from five principal ingredient classes. Fish oils from cold-water marine fish are the most concentrated source: salmon oil typically supplies 8–15 percent EPA + 10–18 percent DHA by total fatty acids per Tocher 2003 (Rev Fish Sci); herring oil 7–12 percent EPA + 5–10 percent DHA; sardine oil 10–18 percent EPA + 9–16 percent DHA; anchovy oil 14–22 percent EPA + 8–13 percent DHA; cod liver oil 7–9 percent EPA + 8–12 percent DHA. Whole fish meals (salmon meal, fish meal, herring meal, sardine meal) supply EPA at lower concentration (typically 1–4 percent of total fatty acids by ingredient weight) but at higher inclusion rates. Krill oil supplies EPA + DHA bound primarily to phospholipid rather than triglyceride per Burri 2015 (Front Aging Neurosci), with EPA + DHA at 8–15 percent combined. Algal oils from heterotrophically-cultivated Schizochytrium, Crypthecodinium, or Nannochloropsis species supply pre-formed EPA and DHA without fish-source dependence. Green-lipped mussel (Perna canaliculus) supplies EPA + DHA + ETA (eicosatetraenoic acid, 20:4n-3, distinct from omega-6 ETA) per Bui 2013 (J Med Food).

The marine source cluster overlaps with our salmon oil explainer, herring oil explainer, sardine oil explainer, anchovy oil explainer, cod liver oil explainer, krill oil explainer, algae oil explainer, fish meal explainer, and green-lipped mussel explainer. The combined omega-3 overlay sits at our omega-3 fatty acids explainer, with the related DHA explainer and DPA explainer covering the other long-chain forms.

AAFCO requirements and therapeutic dose ranges

Per AAFCO 2024 Official Publication Dog Food Nutrient Profiles, canine growth and reproduction formulas require a minimum 0.05 percent combined EPA+DHA on a dry-matter basis (no separate EPA minimum, no separate DHA minimum) plus a minimum 1.3 percent alpha-linolenic acid. Canine adult maintenance formulas have no required omega-3 minimum — an AAFCO position that the WSAVA 2018 Global Nutrition Guidelines treats as a minimum threshold rather than an optimal target, recommending 0.1–0.4 percent combined EPA+DHA on a dry-matter basis for adult dogs based on functional outcome evidence.

Per Roush 2010 (J Am Vet Med Assoc) double-blind randomized controlled trial in 127 dogs with osteoarthritis (177 dog-pair-comparisons across 33 veterinary centers), the therapeutic combined EPA+DHA dose for clinically meaningful symptom reduction (lameness improvement, weight-bearing improvement, owner-reported pain reduction) was approximately 0.43 g EPA + 0.32 g DHA per 1,000 kcal metabolizable energy, equivalent to roughly 40–80 mg combined EPA+DHA per kg body weight per day. ACVIM 2018 consensus statement on canine chronic enteropathies and ACVIM 2024 osteoarthritis guidelines both reference Roush 2010 as the principal dose-finding evidence. Per Mehler 2016 (Prostaglandins Leukot Essent Fatty Acids) and Lenox 2013 (J Vet Pharmacol Ther), the same combined EPA+DHA dose range applies to canine dermatologic inflammatory disease (atopic dermatitis), canine renal disease (CKD), and canine cardiovascular conditions, with condition-specific dose-response evidence varying in strength. The therapeutic dose framework overlaps with our best dog food for joint problems guide, best dog food for skin and coat guide, best dog food for allergies guide, and best dog food for heart disease guide.

Eicosanoid pathway and anti-inflammatory mechanism

Per Calder 2017 (Biochem Soc Trans) and Mehler 2016 (Prostaglandins Leukot Essent Fatty Acids), EPA competes with arachidonic acid (AA, 20:4n-6) for the same cyclooxygenase (COX-1, COX-2) and lipoxygenase (5-LOX, 12-LOX, 15-LOX) enzyme cascades that govern eicosanoid synthesis. COX activity on EPA yields the series-3 prostaglandins (PGE3, PGD3, PGI3, TXA3) which are 50–90 percent less pro-inflammatory than the series-2 prostaglandins (PGE2, PGD2, PGI2, TXA2) derived from arachidonic acid per Calder 2017. LOX activity on EPA yields the series-5 leukotrienes (LTB5, LTC5) which are similarly less pro-inflammatory than the series-4 leukotrienes (LTB4, LTC4) derived from arachidonic acid.

EPA also serves as the precursor for the E-series resolvins (RvE1, RvE2, RvE3) per Serhan 2014 (Nat Med) and Schwab 2007 (Nature). Resolvins are specialized pro-resolving mediators (SPMs) that actively terminate inflammation rather than simply being less pro-inflammatory; the resolvin pathway represents a programmed shift from inflammation initiation to inflammation resolution. The dietary EPA-to-tissue-EPA-to-resolvin pipeline takes approximately 4–12 weeks to reach steady-state in mammalian tissue per Stark 2008 (Prostaglandins Leukot Essent Fatty Acids), which is why omega-3 supplementation trials in dogs (Roush 2010, Lenox 2013) require 8–16 week treatment durations to surface clinical benefit. The inflammation-resolution framework overlaps with our best dog food for sensitive stomachs guide.

How KibbleIQ scores EPA

The KibbleIQ Dry Kibble Rubric treats EPA as a positive ingredient at meaningful inclusion levels. Formulations that list fish oil, salmon oil, herring oil, sardine oil, anchovy oil, krill oil, cod liver oil, or algal oil within the top 15 ingredients earn positive rubric credit on the basis that the inclusion is sufficient to contribute meaningfully toward the WSAVA 2018 0.1–0.4 percent combined EPA+DHA dry-matter target. Formulations that list trace fish-oil flavoring below the omega-3 nutritional minimum earn no rubric credit. Formulations that supply EPA + DHA only via the AAFCO minimum levels (0.05 percent dry matter combined) for puppy growth and reproduction are scored as adequate but not exceptional — the minimum is a floor, not an optimum.

The rubric also evaluates omega-6 to omega-3 ratio for inflammatory balance: typical commercial dry kibble runs omega-6 to omega-3 ratios of 8:1 to 15:1, while WSAVA 2018 recommends 4:1 to 6:1 and ACVIM 2018 consensus supports tighter 2:1 to 4:1 in inflammatory disease management contexts. Formulations meeting tighter omega-6 to omega-3 ratios earn additional positive credit per Bauer 2011 inflammatory balance framework. To check whether your dog’s food supplies meaningful EPA, paste the ingredient list into the KibbleIQ analyzer. For methodology context, see our published methodology. For peer omega-3 context, see our DHA explainer, DPA explainer, and combined omega-3 explainer.