interesting... neem oil. I had to look that one up! Apparently, you don't want your breeding roosters dusting in it?
"Studies done when Azadirachtin (the primary active pesticidal ingredient in neem oil) was approved as a pesticide showed that when neem leaves were fed to male albino rats for 11 weeks, 100% (reversible) infertility resulted."
I haven't had an issue with infertility. I check the eggs I crack and nearly all of them have been fertilized. If you use the neem with roos, I guess just check the eggs and see if you're dropping in fertility rates? I do use it with my roos.