I have a flock of 20 hens hatched May 16th. I treated them with Piperazine when they were 6 weeks old. (I always wormed puppies at regular intervals) I haven't started to get eggs yet-though soon I'm sure. What I want to know is should I go ahead and Ivermectin them before they start to lay or just treat as needed? I hate to think they are walking around with parasites. I would think they could decline quickly?