1. Hannah Ritchie and Max Roser, Meat and Dairy Production, published in August 2017; last revision in November 2019, https://ourworldindata.org/meat-production
2. Kemp, B., and M. W. A. Verstegen. 1987. The influence of climatic environment on sows. In: M.W.A. Verstegen and A.M. Henken (eds.) Energy metabolism in farm animals effects of housing, stress and disease. p 115. Martinus Nijhoff, Dortrecht.
3. Cristina M. Santanaa, Phillip Gaugera, Amber Vetgera, Drew Magstadta, Dong-Suk Kima, Denusha Shresthab, Chandrashekhar Charavaryamathb, and Wilson K. Rumbeihac, Ambient hydrogen sulfide exposure increases the severity of influenza Avirus infection in swine, Mar 2021
4. REGULATION № 44 FROM 20 APRIL 2006 FOR VETERINARY MEDICAL REQUIREMENTS FOR LIVESTOCK FACILITIES of the Ministry of Agriculture in Bulgaria
5. Regulation of Minister of Agriculture and Rural Development of 15 February 2010 on the requirements and the manner of keeping of farm animal species for which protection standards are laid down in the provisions of the European Union;J Laws,2010