i have gone down that road also and it's not harmed mine, they win or score frequently and more importantly they have not had ybs or any other illness. at the start of the season this year i had them tested (throat swabs+droppings) from stock,young+old racer's and the only thing that showed up was worms in some of them. i did then treat for that. but we topped the fed a week before testing and 2 weeks after. i had them tested for piece of mind,you hear so many things going about. i also think that to many people are giving antibiotics for a performance boost . i think if used only when needed there's no problem but you hear of people giving some form of antibiotic every week which i think is a bad thing.