When farmers raise fast growing breeds of chicken they may claim "slow grown" and this may not be the case.
There are many fast growing breeds of chicken and since the consumer is becoming more informed about these types of breeds, more breeds are being developed. Some take as little as 3 weeks to make ideal market weight and the so called slower breeds may take 8-10 weeks to reach ideal market weight.
Any chicken under 12 weeks of age is not nutritionally dense, by any means. In nature baby chicks take their time developing, this gives their body time to adjust and allow their organs, muscles and bones to develop properly. Hens do not lay eggs until they mature. This means that they are not using every ounce of food to develop muscles, strong organs, healthy bones and a fully developed central nervous system. Now they can begin to utilize the food as energy and lay eggs. Depending on the breeds, hens begin to lay eggs anywhere from 12-16 weeks of age. When we eat chickens that are from faster growing breeds, and under 12 weeks of age, we are eating a bird that is still utilizing all the food for growing. There is not enough stored nutritional density in that chicken to provide the consumer with a nutritionally dense source of nutrients.
We are preserving old fashioned heritage breeds vs. most small family farmers who participate in the extension of factory farming by raising commercial & fast growing commodity breeds. Heritage breeds are better for the ecological system, are naturally slow-grown and produce superior nutrient-dense proteins, fats & bone marrow.