They dont know, but the final conclusion was this:
Supplementation of NaHCO3 may prolong persistency of maintaining a profitable egg production during the late laying period.
More research would have to be done to make anything conclusive about the benefits of adding baking soda.
Agree, its just not a significant difference. Which I understand could make a difference for keeping battery hens and the bottom line. For people with a few hens in the backyard the risks outweigh the rewards and they wouldn't see a difference in egg production or health and could have...
The ones I read show mixed results and not significant improvements in laying.
https://www.tandfonline.com/doi/abs/10.1080/00071669208417527
https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=6f0ba7345af35997f612894a3ac94c5ed60113d9...