Oxidation is a significant problem in omega-3 oils sold for pets, with multiple studies showing that a notable percentage of these supplements are rancid and may lose potency or even become harmful.[1][2][3][4]
Data on Oxidation in Omega-3 Pet Oils
- A 2025 peer-reviewed study showed that 45% of popular omega-3 supplements (including those for pets) tested positive for rancidity.[4]
- In a large New Zealand market survey, about 28% of tested fish oil products exceeded peroxide value (PV) limits (primary oxidation), 14% exceeded anisidine value (secondary oxidation), and 23% exceeded total oxidation (TOTOX) limits for unflavored products.[2]
- Additional studies from other regions found similar results, with up to 73% of over-the-counter omega-3 supplements exceeding accepted peroxide safety levels in some markets (not pet-specific, but likely generalizable due to similar production practices).[1]
Harm Caused by Oxidized Omega-3 Oils
- Rancid/oxidized omega-3 oils can produce free radicals and lipid peroxides. These compounds may harm cells, proteins, and DNA, leading to increased inflammation, immune compromise, premature aging, and an elevated risk of chronic diseases such as cancer.[3][5]
- In pet-specific contexts, research shows that consuming oxidized oils may worsen arthritis, allergies, and increase cancer cell formation in animals, rather than providing the intended anti-inflammatory benefits.[3]
- Experts agree that rancid fish oil is worse than none at all: its consumption can exacerbate the risk of disease rather than offer health improvements.[5][6]
Key Numbers and Takeaways
| Finding | Value | Source |
| Products exceeding peroxide limit (PV) | 28% (unflavored NZ oils) | [2] |
| Products exceeding total oxidation (TOTOX) limit | 23% (unflavored NZ oils) | [2] |
| Supplements testing positive for rancidity | 45% (popular market products, 2025) | [4] |
| Products above peroxide safety limits (other regio) | 73% (SA market, likely similar to other OTC oils) | [1] |
Practical Advice for buying Omega-3s for pets
Buy omega-3 oils only in dark, airtight packaging, and avoid products in plastic bottles. Look for brands with published oxidation values and third-party testing data.[6][5]
Consider refrigerated or single-use capsule formats and consume rapidly after opening to limit oxidation.[5]
Safe Alternatives:
- Fresh cold-water fish – raw is the best way to feed this for its omega-3 content however many fish products should not be fed raw as they contain pathogens – if you chose to feed fish gently cook the fish but understand that the heat will diminish the omega-3’s in the food.
- PhytoSmart Omega DHA, DHA/EPA or Celle-Abrate health – this is the only whole food, un-extracted Omega-3 superfood supplement that is made from whole cell algae and contains the highest level of bio-available omega-3 fats for pets and all mammals. It comes in an easy to dispense shaker top jar – just shake it on top of your pet’s food and provide them with whole food unextracted algal omega-3’s made from un-processed marine microalgae.
- Green-lipped mussel oil-may be less prone to oxidation if they are shipped and stored properly, this may be safer for pet health if you feel the need to feed an oil – it is expensive and you will need to feed large amounts to get the benefits – be cautious with pets prone to digestive upset.[3]
Oxidation is common in omega-3 oils for pets, with nearly half of products in some studies failing freshness standards. Oxidized oils can significantly harm pets by increasing inflammation, damaging cells, and undermining the very health benefits they are meant to provide.[2][4][5][3]
Sources
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4678768/
- https://www.nature.com/articles/s41598-017-01470-4
- https://fettlepets.com/blogs/news/why-we-will-never-sell-salmon-oil-to-support-your-pets-health
- https://smhs.gwu.edu/news/tests-find-many-popular-omega-3-supplements-are-rancid
- https://thenaturaldogstore.com/blogs/health/fish-oil-for-dogs-risky-or-beneficial
- https://drjudymorgan.com/blogs/blog/most-pet-diets-are-deficient-in-omega-3-fatty-acids
- https://www.sciencedirect.com/science/article/pii/S0006291X16321878
- https://goedomega3.com/storage/app/media/scientific-reports/Oxidation in Omega-3 Oils_ An Overview.pdf
- https://pmc.ncbi.nlm.nih.gov/articles/PMC3657456/
- https://onlinelibrary.wiley.com/doi/full/10.1002/lite.201600013