Like fish oil, flax seed oil is used to treat chronic inflammatory disorders. Fish oil is a direct source of EPA and DHA whereas the ALA within flax seed oil must be converted into DHA and EPA. However, many species of animals (probably including dogs and cats) and some people cannot efficiently convert ALA to the more active non-inflammatory omega-3 fatty acids (EPA and DHA). As a result, the anti-inflammatory effects of flax seed oil may not be as strong as the anti-inflammatory effects of fish oil.
The use of flax seed oil unrelated to its anti-inflammatory effects is as a dietary source of soluble fiber. Increasing soluble fiber in the diet can help counter tendencies to constipation. Read more.