Animals are raised in concentrated animal feeding operations (CAFOs) known as factory farms.
Hundreds to millions of animals, usually dairy cows, pigs and chickens, are packed into massive windowless buildings where they are confined in boxes or stalls.
These factory farms produce huge amounts of animal sewage and other pollutants.
The quantity of urine and feces from the smallest factory farm is equivalent to the urine and feces produced by 16,000 humans.
The waste contains disease-causing pathogens, chemicals, pharmaceuticals and heavy metals.
Over 168 gases are emitted from the waste, including hazardous chemicals such as ammonia, hydrogen sulfide and methane.
Airborne particulate matter carries disease-causing bacteria, fungus or other pathogens.
Animals frequently die in factory farms, and their broken, lifeless bodies contribute to the waste.