my brand new puppy has fleas so i got him a hartz flea and tick collar to treat him. but soon, he pooped diahrea and then a few hours after he pooped diahrea with blood!!!!!! also my brand new puppy i got, he pooped the bloody diahrea often. so i warn you all with small puppies/dogs do not use the hartz brand. it might depend on the dog but i would not risk it!!!!!!!