What's true for humans is also true for chickens - the natural antiseptic properties of propolis have been proven beneficial for numerous species...
Effects of Propolis on Eggshell Microbial Activity, Hatchability, and Chick Performance in Japanese Quail (Coturnix coturnix japonica) Eggs
Poultry Science, 2012 April
Propolis is a sticky resin produced by worker honeybees from substances collected from plants, and it has strong antibacterial and antifungal properties.
The purpose of this study was to establish the effects of propolis on egg weight loss, hatchability, chick performance, and to control microbial activity naturally occurring on eggshells.
A total of 750 fresh eggs was randomly divided into 5 groups. Eggs from the first group were sprayed with ethyl alcohol (70%, A), the second group was sprayed with benzalkonium chloride (B), and the third, fourth, and fifth groups were sprayed with propolis at 3 doses: 5, 10, and 15%. Eggs sprayed with propolis had lower egg weight loss than eggs from groups A and B (P < 0.001). Bacterial activity was reduced significantly in all propolis groups. There were no significant differences between treatments for hatchability, embryonic mortality, BW gain, and relative growth.
Results of the present study indicated that propolis could be an alternative hatching egg disinfectant versus a chemical disinfectant, without adverse effects on hatchability and performance of quail chicks.