Animals on factory farms are treated like meat, milk, and egg machines. Chickens have their sensitive beaks seared off with a hot blade, and male cattle and pigs are castrated without any painkillers. All farmed chickens, turkeys, and pigs spend their brief lives in dark and crowded warehouses, many of them so cramped that they can't even turn around or spread a single wing. They are mired in their own waste, and the stench of ammonia fills the air. Animals raised for food are bred and drugged to grow as large as possible as quickly as possible—many are so heavy that they become crippled under their own weight and die within inches of their water supply.
Animals on factory farms do not see the sun or get a breath of fresh air until they are prodded and crammed onto trucks for a nightmarish ride to the slaughterhouse, often through weather extremes and always without food or water. Many die during transport, and others are too sick or weak to walk off the truck after they reach the slaughterhouse. The animals who survive this hellish ordeal are hung upside-down and their throats are slit, often while they're completely conscious. Many are still alive while they are skinned, hacked into pieces, or scalded in the defeathering tanks. Learn more about the factory-farming industry. By switching to a vegetarian diet, you can save more than 100 animals a year from this misery.
From PETA : http://goveg.com/vegetarian101.asp