Free range chickens that eat plenty of insects will have more EPA/DHA (Omega 3) than chickens fed flax seed. Flax (linseed) contains the precursor to EPA/DHA in the form of ALA and LA (linoleic acids), which must be converted into EPA/DHA in the chicken's body (same thing happens in humans). The problem is, the conversion rate is very low, under 10% usually, so more flax must be given to get the same level of O3 fats. If they get enough insects, especially crickets and grasshoppers (any leaf eating bug, really), the bug has already converted the plant's LA/ALA into EPA/DHA, so the chicken doesn't have to convert it. Fish oil is good (no conversion), I just wouldn't know how to deliver it to the chicken (feed them sardines!). And you might need to consider cost as well. At any rate, just let chickens be chickens, and let them eat lots of bugs!