Two of my favourite authors are Robb Wolf author of The Paleo Solution and Claire Yates author of Optimum Health the Paleo Way both present amazing information about the importance and difference between the grass-fed option and the grain-fed or finished choice of meat.
Claire Yates makes the point that animal and humans alike thrive on the diet that they are designed to or evolved to eat. Domesticated animals that are fed a diet of soy, corn, and protein meal, or synthetic vitamins impacts on the health of the animals. This is reflected in the quality of fats and nutrients within the meats. Yates suggests that the dependence on using a grain based diet with the production of animals provides a faster fattening up period for production but which makes the fats pro-inflammatory. This is when the balance of omega 3 to omega 6 that is stored in the animals fat is out of balance. Consider that seed oils like canola are mostly omega 6. If you feed a cow corn or other grains the absorb the omega 6 and it crowds out the omega 3’s that the animal would have been producing in their fats from the natural grass grazing diet. The meat produced is also leaner and the fat has a slightly yellow colour to it because of all the beta carotene from their natural diet.
My own research as lead me to read and summarise that biggest factor about cows not eating a natural diet is that the digestive system of the animal does not cope with digesting grain. The stomach acid and bacteria in a cows stomach is not able to support this type of diet long term without developing life threatening stomach condition, bloat, excessive gas production and a compromised immune system. To keep the animals health the farmers are reduced to using steroids and antibiotics to keep the animal alike long enough for slaughter.
This type of food production used to feed animals a diet outside of their natural diet for profit and faster products is also not limited to but includes fish farming. At this point I understand that the only animal likely to do is the poultry. It is the nature of chicken’s digestive system that they can break down the grains better than other animals but they still require a predominantly grass-fed or free-range diet.