In general, animals that eat grass and things that eat grass (insects, mostly) will have a much higher amount of Omega 3s than those that eat mostly corn and ground up animal byproducts.
Even we humans have a ton more omega-6 in our tissues than we did before, largely because of our diets. In 1961, we ate diets of 5.8% omega-6s, and our adipose tissue concentrations of n-6 were 9%. Today, Americans eat around 9% of their energy as n6 fats, and they are 23%+ of our fat tissue!