Galal, A., A.M.H. Ahmed, W.A.H. Ali, M.H. El-Sanhoury, and Hedia E. Ahmed. 2008. “Residual Feed Intake and Its Effect on Cell-Mediated Immunity in Laying Hens Given Different Propolis Levels”. International Journal of Poultry Science 7 (11): 1105–1111. https://doi.org/10.3923/ijps.2008.1105.1111.