1. BP. Statistical review of world energy 68th edition. 2019: 1-62.
2. Ritchic H, Roser M. (2017, 2019-8-26). Number of animals slaughtered for meat. Available: https://ourworldindata.org/meat-and-seafood-production-consumption.
3. FAO. (2019, 2019-8-10). Nitrogen inputs to agricultural soils from livestock manure (3 May 2019 ed.). Available: http://www.fao.org/economic/ess/environment/data/livestock-manure/en/.
4. United States Environmental Protection Agency. Literature review of contaminants in livestock and poultry manure and implications for water quality. National Service Center for Environmental Publications (NSCEP) 2013: 1-137.
5. Cox D. (2019, 2019-3-25). The planet's prodigious poo problem. Available: https://www.theguardian.com/news/2019/mar/25/animal-waste-excrement-four-billion-tonnes-dung-poo-faecebook.