I wormed my chickens, about a month and a half apart from first to last, and they live in an area, where they can easily eat each other's poop. Will the worms become resistant if they eat a recently wormed chicken's poop, and the amount of residue they eat is way less than the recommended dosage? My mom's dog also ate my cat's poop, and he is recently been dewormed. I last use dewormer on my mom's dogs about 3 weeks ago, and I think they have some roundworms again but they are still in larvae form in their body. How long does it take for parasites on chickens and dogs to become resistant to a drug if they are underdose? Please provide a link.