tail chsing

Question
i have a 3 month old puppy who has recently started chsing his tail. He has white marking all over him and one of them just happens to be at the very tip of his tail, i believe that when he wags his tail he can see a white thing moving in the corner of his eye, so he then hust launches at it. What can i do to stop this? he cant be bored, as i have a 5 year old dog at hom aswell and they play together. any ideas, i dont know what to do. do you think he is doint it because of his white tip??

Answer
While a white tipped tail is common, many dogs chase their tail that don't have white tipped tails.  Certainly many of my Labs have, and only one of them had a white tipped tail.  My 4 month old Xanthe has been chasing hers this morning.  

While your puppy does have the 5 year old to play with, the 5 year old may not want to spend as much playing as the 3 month old.  The 3 month old will go, go, go, until it collapses.  In all but the most severe cases, it is best just to let the puppy out grow it.