I came across a study comparing the nutritional values of chicken based on various farming practices. I'm only going to focus on the two best ones, Pastured Chicken vs Free Range, Organic. Just to clear things up, I'll give a quick description of the two farming practices.
Free Range, Organic - This is the best chicken you will find at most grocery stores across America. Free Range means that the chickens are not in individual cages and are free to roam around in a large house full of thousands of birds. They have access to a fixed small outside yard that is likely just dirt as the chickens will have eaten every last bit of vegetation. The Organic label means that the feed provided meets the USDA Organic standard, Non-GMO, no chemicals, etc. Also, the chickens aren't given any antibiotics.
Pasture-Raised Chicken - This is what we produce. These chickens are raised outdoors on pasture. They are typically housed in bottomless tractors (see image) which are moved frequently (at least once a day) to provide access to fresh grass, new bugs, and clean pasture. Any type of feed can be used; however, we use a premium Non-GMO feed tested to be free of all the commonly used chemicals. We also never give antibiotics to our birds.
This study focused on several key elements of nutrition that are improved when animals are raised on pasture.
Omega 6:3 Ratio - This is the ratio of Omega 6 to Omega 3 Fatty Acids. While we need both types, the typical American diet is far too heavy on Omega 6 Fatty Acids. This causes inflammation and leads to a number of long-term health risks. The typical American diet provides a total intake ratio of 25:1 or worse. Ideally, it is recommended to consume a ratio of 4:1 or less. Some even advocate for a ratio of 1:1.
Vitamin D - Vitamin D3 is obtained from the sun. Since chickens from most farming practices (including conventional farming methods and Free Range) rarely see sunlight they don't contain measurable amounts of Vitamin D3.
Vitamin E - Vitamin E acts as an antioxidant and is beneficial to many organs.
The following table shows the results of their analysis along with the USDA National Database Standard Reference.
In conclusion, while Free Range, Organic chicken is probably the best chicken available at your local grocery store, it still doesn't compare to pasture-raised chicken. Pasture-raised chickens have a better Omega 6:3 ratio, much higher Vitamin D3, twice the levels of Vitamin E and less cholesterol. The reason is simple: pasture-raised methods provide key elements including fresh vegetation, bugs, exercise, and sunshine. These sound like basic things, but simply aren't available to large scale, factory farm produced chickens. There is no room for those things in the "10k birds in a house" model. I'll leave you with a final question to reflect on. How healthy would you be if deprived of salads, exercise, and sunshine?