"Like pornography, factory farming is hard to define but easy to identify. In a narrow sense it is a system of industrialized and intensive agriculture in which animals - often housed by the tens or even hundreds of thousands - are genetically engineered, restricted in mobility, and fed unnatural diets (which almost always include various drugs, like antimicrobials). Globally, roughly 50 billion land animals are now factory farmed every year. (There is no tally of fish). Ninety-nine percent of all land animals eaten or used to produce milk and eggs in the United States are factory farmed. So although there are important exceptions, to speak about eating animals today is to speak about factory farming."
-Jonathan Safran Foer, Eating Animals, 2009
This book is the reason I became a vegetarian, so insightful.