Livestock production is one of the major agricultural industries in the U.S. Dairy, beef, swine, and poultry dominate production, but other livestock such as sheep, goats, and horses among others are also produced. The over 9 billion head of livestock (105 million cattle, 62 million pigs, 9.3 billion chickens and turkeys) generate an estimated 145 million tons (dry matter) of livestock manure, 64 million of which (10.65 million in beef feedlots; 21.3 million tons in dairy; 6.1 million in other cattle; 17.5 million in poultry; 8.6 million in swine) is produced by animals that are confined and which must be collected and disposed of.
Most livestock manure is currently used as fertilizer for crops and pasture, however, for a number of counties, the amount of livestock manure produced exceeds the nitrogen or phosphorus nutrient assimilative capacity of the soils leading to fertilizer runoff and a need to develop alternative methods of manure disposal. One alternative is the use of manure to produce bioenergy and bioproducts using technologies such as anaerobic digestion (for liquid manures that are typical in dairy and swine production), and gasification and pyrolysis (for solid manures that are common in beef and poultry production). Components of livestock manure can also be recovered to produce bioproducts.
The EPA estimates that as of 2005, approximately 2,623 dairy farms (38% in California and 80% in the top 10 dairy states), and 4,281 swine farms (51% in North Carolina and Iowa and 85% in the top 10 swine states) were good candidates for biogas collection and bioenergy production.