Vargas-Rodriguez , L.M., J.G. Herrera, E.J. Morales, J.L. Arcos-Garcia, R. Lopez-Pozos, and G. Ruelas. 2015. “Effect of Citric Acid, Phytase and Calcium in Diets of Laying Hens on Productive Performance, Digestibility and Mineral Excretion”. International Journal of Poultry Science 14 (4): 222–228. https://doi.org/10.3923/ijps.2015.222.228.