Musapuor, A., et al. “The Effects of Phytase and Different Level of Dietary Calcium and Phosphorous on Phytate Phosphorus Utilization in Laying Hens”. International Journal of Poultry Science, vol. 4, no. 8, July 2005, pp. 560–562, https://doi.org/10.3923/ijps.2005.560.562.