I'm doing research for a website on organic food that I'll be building next year. What I'm learning is mind-boggling. Notice the highlighted sentence below on the grain it takes to feed the birds, and how we use more grain than we get back in meat.
Legacy of farming methods comes home to roost - Opinion - smh.com.au:
It isn't called 'factory farming' merely because those sheds look like factories. Everything about the production method is geared towards turning live animals into machines for converting grain into meat or eggs at the lowest possible cost.
Walk into such a shed and you will find up to 30,000 chickens. The National Chicken Council, the trade association for the US chicken industry, recommends a stocking density of 85 square inches (548 square centimetres) a bird - less than a standard sheet of typing paper.
Environmentalists say that this production method is unsustainable. It relies on the use of fossil fuel energy to light and ventilate the sheds, and to transport the grain eaten by the chickens. When this grain, which humans could eat, is fed to chickens, they use some of it to create bones, feathers and other body parts that we cannot eat. So we get less food back than we put into the birds - and less protein, too - while disposing of the concentrated chicken manure causes serious pollution to rivers and ground water.
It's short article, worth a read.