I've heard lots of pros & cons about this. Right now there are many birds in the laying flock molting, and they're not producing many eggs. There was a bad infestation of roundworms early this summer & I gave them both Wazine & Ivermectin pour-on then. I've taken their water away tonight & am seriously considering giving them another dose of Wazine tomorrow. And if Ol' Murphy is listening, he'll make them start laying more while I'm waiting for the withdrawal period to end!