I feed mine plani yogurt as a treat, maybe once a month, mixed with their feed, I have not seen any symptoms appear from doing so. I have a handful of hens that are 6-8 years old and still laying eggs pretty consistent and are just as healthy as the pullets. Personally, I think over abundance of any one thing is not healthy, whether it be for humans, animals or nature, so I prefer mixing things up, espeically with their feed and treats, and they surely let me know what they want, what they like and what their system needs. (like dogs and the tall grass blades, cant force them to eat them when everything is in check, and you cannot get them to stop when their tummies are upset) If something is working, why try to fix it? I often wonder if the media tries to persway us in many of the choices we make in our lifestyle and uprearing. So many things that we have been told in the past that were tabu are now "recommended". I say, stick to your instincts, if you see positive results from feeding them yogurt, then go for it. If you have doubts and see that they are not getting the results desireded, stop.