Honestly, I originally started hearing about it from social media, but of course, who trusts that now-a-days, so I did some superficial research.
This was a study done by World's Science Poultry Journal. I only mention this because researchgate seems to be hit and miss with reliability of the studies it publishes, but WSPJ seems to be a fairly reliable source.
https://www.researchgate.net/public...ropolis_as_a_natural_feed_additive_in_poultry
This study showed propolis lowered bacterial count in egg shells and helped with shelf life of eggs.
https://pubmed.ncbi.nlm.nih.gov/34817037/
This next study was done to see how propolis affected the fatty liver of caged egg-laying chickens who are fed high-energy feed. That doesn't apply to mine specifically, but it does show some benefits of it. How those benefits compare to a chicken raised in a coop with access to a run? Unknown.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10539770/
It seems promising, but I'm not a scientist and haven't done any experimenting, so I was just wondering if anyone out there had tried using it and if they saw any results.