Galal, A.; El-Motaal, A. A.; Ahmed, A.; Zaki, T. Productive Performance and Immune Response of Laying Hens As Affected by Dietary Propolis Supplementation. Int. J. Poult. Sci. 2008, 7 (3), 272–278. https://doi.org/10.3923/ijps.2008.272.278.