Losada H, Pealing R, Cortés J and Vieyra J 1997: The keeping of poultry and pigs in the backyards of the urbanised areas of Iztapalapa (east of Mexico City) as a proposal for sustainable production. Livestock Research for Rural Development. Volume 9, Article #28. Retrieved , from http://www.lrrd.org/lrrd9/3/mex932.htm