Hello!
I don't have the info you are looking for but I'd be interested to see if Aoxa has any info.
My personal thought (based on some extensive reading on issues of the immune system and various thoughts on the subject of building a strong immune system) ...on chickens eating worms, bugs, etc., is that it is something that they would do in their natural environment.
Bugs, birds, animals and their droppings, and all kinds of other various things in the environment can always have the possibility of carrying various diseases. However, if the chickens are healthy with a strong immune system they are designed to come into contact with all those things and thrive. It's when they are weakened by unnatural feed, over-crowding, indiscriminate, regular use of medications, various immunizations, wormers, constant "sanitation" of the environment, etc., that they become weakened and are unable to fight off the things that they'd be exposed to in nature on a regular basis.
This is one of those things that we are "re-learning" in human medicine. When children are exposed to the environment, allowed to get dirty, come in contact with germs, etc., it appears that they have a stronger immune system and are able to more easily deal with various illnesses. Those that have been "kept clean", not allowed to play, have to wash with antibacterial soap every time they come into contact with a little dirt or a piece of raw meat or....etc.... they are now realizing don't have the same kind of opportunities to strengthen their immune systems in quite the same way. Add the constant use of antibiotics - which has led to MRSA and other resistant strains, and we have a real problem on our hands.
Anyhow....
I firmly believe that we - and our animals - were created to thrive in a "natural environment". Part of that would be running out in the dirt and grass, eating worms, grasshoppers, plants and whatever else they can find. And in the process building strong immune systems. So I try my best to "mimic" as best as possible what they'd do if they were free.
Too bad I couldn't let them migrate further south this winter
(Okay...off the
)
Edited to add: I used the term "poor" or "unnatural" feed which in my thinking is any feed that is primarily plant based and includes soy and other legumes. So at some level all of our birds are compromised in the feed area unless we make a definite effort to balance it with animal/insect protein and lower the percentage of grain/legume type feeds. This, of course, is helped tremendously by their being allowed to range and eat a more natural diet including insects and plants they choose in the warm months at least. And that's why I mentioned letting them migrate south...because I have a hunch they would have started following the food to warmer climates a long time ago!!!