You are right. The article does say that! Chickens don't build resistance, but some do believe they can carry a load and not be effected. Worms are parasites, so controlling them is the best thing to do.That article states: "Chickens older than 4 months develop resistance to roundworms; the mature chicken’s immune system kicks out most of the bums." I've read similar sentiments elsewhere. So I started treatment today on all the whole flock and will do the 5-day course. In handling them all within a short time tonight, I noticed that a few felt skinny to me. I think worming was overdue. Fingers crossed.
But now I have a new problem -- baldness on my Australorp this evening. See attached pic. She was absolutely positively NOT bald this morning. I checked her all over for mites, etc. and see nothing. Her skin is not irritated at all. Despite being the biggest chicken, she is very low in the order.
I think I have a very big bully. And I suspect it is my BO.
Do you happen to have a rooster?
If not, then likely a dominant hen is pulling feathers. I would just keep watch on it. Do they have plenty of space?