Ugh.
ONLY FEED RODENTS, etc. from good sources. Never feed anything you catch, or find, etc! Forget the poison, you are asking for other illnesses and/or parasites in wild animals.
Additionally, unless you want to breed your own rodents, I would advise caution on who and where you buy live rodents from. Wild caught rodents are not the only ones who can have health issues that can spread to your animal.
Another reason why I encourage, and feed all my animals, Frozen/Thawed (F/T) prey. The freezing process kills most things that could hurt your your animal and there are quite a few reputable F/T feeder breeders out there.
Again, know the source of your prey items, and feed F/T if your snake will tolerate it.