Flaxseed in dog and cat food
Flaxseed, also called linseed, is the seed of the flax plant. Pet foods usually add it ground, as a plant source of the omega-3 fatty acid alpha-linolenic acid (ALA) that also brings fibre and protein. Dogs absorb the ALA and turn some of it into EPA, but little or none into DHA, the longer omega-3s found in fish oil. Cats appear to convert even less. EU feed law caps hydrocyanic acid, a natural plant toxin, in linseed.
Is it OK for dogs and cats?
- Dogs
- There is no known concern at the amounts used in complete foods. Flaxseed raises ALA and some EPA in dogs' blood. But studies found no DHA increase and no rise in the omega-3 index (EPA plus DHA in red blood cells). So it does not replace marine sources such as fish oil when EPA and DHA are the aim.
- Cats
- There is no known concern at the amounts used in complete foods. In a 28-day study of 20 cats, food with 2.6% added ground flaxseed raised blood ALA with no change in stool quality or nutrient digestibility, though total stool output rose. Cats appear to have low activity of the enzyme needed to turn ALA into EPA and DHA, so flaxseed mainly supplies ALA itself.
How settled this is: No known concern at the amounts used in complete foods
What flaxseed is
Flaxseed and linseed are two names for the seed of the flax plant, Linum usitatissimum. The EU Catalogue of feed materials lists linseed as whole, flattened or ground seed. It lists the products left after oil manufacture separately: linseed expeller, also called cake (after pressing), and linseed meal (after extraction). Most pet foods that use flaxseed use the ground whole seed.
Why it is in pet food
Flaxseed is added mainly as a plant source of omega-3 fat (ALA). It also adds fibre and protein. FEDIAF and AAFCO set minimum ALA levels for dogs and cats during growth and reproduction. Plant sources of ALA, such as flaxseed oil, are discussed as a more sustainable complement to fish oil.
What it does in the food
A 2022 study cites flaxseed as containing about 23% ALA, 6.5% linoleic acid (an omega-6), 20% protein and 28% fibre, plus lignans. In dogs fed a flaxseed diet for 84 days, blood ALA, EPA and DPA rose within 4 days, but no DHA was found. In another dog study, flaxseed cake (the seed with most of its oil removed) did not raise the omega-3 index after four weeks, while fish and krill did. Cats have limited, possibly absent, activity of the delta-6 desaturase enzyme needed for this conversion. Even so, some long-chain omega-3 production has been shown in cat liver and brain. ALA may also have anti-inflammatory effects of its own, apart from conversion. The 2022 cat study notes that oil typically gives greater ALA uptake than ground seed, citing research in people.
Safety and limits
EU feed law lists hydrocyanic acid (cyanide) as a natural plant toxin. It caps it at 250 mg/kg in linseed, 350 mg/kg in linseed cakes, and 50 mg/kg in complete feeds such as pet foods (values at 12% moisture). Cats fed 2.6% ground flaxseed for 28 days showed no change in stool quality or digestibility, though total stool output rose, which the authors linked to the added fibre. In dogs, some studies of flaxseed products have found lower nutrient digestibility. In one study in working dogs, digestibility fell as linseed cake rose to 8% of the diet; the authors judged up to 4.2% well tolerated. ALA oxidises more readily than linoleic acid, so the fat in flaxseed can change during storage.
What depends on the amount and the recipe
How much ALA a pet absorbs depends on the form: oil is reported to give more than ground seed, and most pet foods use ground whole seed. What the ALA does depends on the species: dogs turn some of it into EPA, while cats appear to convert little. The amount matters for digestion, since larger amounts of flaxseed products can lower digestibility and increase stool output. Freshness and storage matter because ALA oxidises easily. In the EU, linseed must also meet the hydrocyanic acid limit.
Not the same as
- Flaxseed oil (linseed oil) — The pressed oil only, without the seed's fibre and protein. In one published table, cold-pressed flaxseed oil was about 53% ALA.
- Linseed meal, linseed expeller or linseed cake — What is left after oil is extracted or pressed from the seed. The EU catalogue lists these separately from linseed. One of the dog studies used flaxseed cake, not the whole seed.
Also printed as
flaxseed · ground flaxseed · flax seed · ground flax seed · linseed · ground linseed · whole flaxseed · whole ground flaxseed · milled flaxseed · golden flaxseed · brown flaxseed
Related
Sources
- Commission Regulation (EU) No 68/2013 on the Catalogue of feed materials, consolidated text of 24 July 2022 (entries 2.8.1 to 2.8.3) — European Union (EUR-Lex), 2022. Linseed is the seed of Linum usitatissimum as whole, flattened or ground seed; linseed expeller (pressed) and linseed meal (extracted) are separate entries; the term 'expeller' may be replaced by 'cake'.
- Directive 2002/32/EC on undesirable substances in animal feed, consolidated text of 28 November 2019, Annex I Section III (inherent plant toxins) — European Union (EUR-Lex), 2019. Hydrocyanic acid is listed as an inherent plant toxin; maximum 250 mg/kg in linseed, 350 mg/kg in linseed cakes, 50 mg/kg in complete feed (10 mg/kg for young chickens), relative to 12% moisture.
- 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 45(1):1-10 — PubMed (Springer/AOCS journal), 2010. Dogs fed a flaxseed diet for 84 days had higher serum ALA, EPA and DPA by day 4, but no DHA was found.
- Lindqvist H et al. Comparison of Fish, Krill and Flaxseed as Omega-3 Sources to Increase the Omega-3 Index in Dogs. Veterinary Sciences 10(2):162 — PubMed (MDPI journal), 2023. After four weeks, the omega-3 index rose in dogs fed krill meal or fish meal/oil but not in dogs fed flaxseed cake. Study sponsored by a krill producer; four of five authors employed by the sponsor.
- Panasevich MR et al. Dietary Ground Flaxseed Increases Serum Alpha-Linolenic Acid Concentrations in Adult Cats. Animals 12(19):2543 — MDPI (peer-reviewed journal), 2022. 2.6% ground flaxseed for 28 days raised serum ALA in 20 cats with no change in stool quality or digestibility; total faecal output rose; flaxseed composition (about 23% ALA, 6.5% LA, 20% protein, 28% fibre, lignans); most pet foods use ground whole flaxseed; oil typically gives greater ALA bioavailability (citing a human study); cats have low delta-6 desaturase activity but some long-chain omega-3 synthesis in liver and brain; flaxseed products lowered digestibility in some dog studies, linseed cake up to 4.2% well tolerated in working dogs.
- Burron S et al. The balance of n-6 and n-3 fatty acids in canine, feline, and equine nutrition: exploring sources and the significance of alpha-linolenic acid. J Anim Sci 102:skae143 — Oxford University Press (peer-reviewed journal), 2024. Cats have limited or null delta-6 desaturase activity; dogs convert some ALA to EPA and to a limited extent DHA; ALA cannot maintain tissue EPA and DHA at levels equal to marine sources; ALA's effects on inflammation may be independent of conversion; FEDIAF and AAFCO set minimum ALA levels for growth and reproduction; ALA-rich plant oils such as flaxseed oil as a sustainable option; ALA is more susceptible to oxidation than LA; cold-pressed flaxseed oil 53.4% ALA.
Checked against these sources on . Definitions are in our own words. This is a reading aid, not veterinary advice: a vet who knows your animal comes first.