You know to be careful with poison, right? If the mice eat it and then run off anywhere to die where the chickens can get them, the chickens will die too...
I don't think the print looks "human" enough to be raccoon, the fingers are too short and the print is just too wide and stubby. I'm actually thinking skunk. A googling I shall go!
ETA: uncertain, inconclusive. A possibility, nothing more. The only skunk prints I can find on line somewhat...