How old is Ava?
In young dogs, tail chasing can be part of normal play behavior, but in older dogs it can be a sign of a variety of things: boredom, lack of exercise, anxiety, or even neurological problems.
There's a good (brief) article on it here -
http://www.usask.ca/wcvm/herdmed/applied-ethology/behaviourproblems/tailchase.html
In young dogs, tail chasing can be part of normal play behavior, but in older dogs it can be a sign of a variety of things: boredom, lack of exercise, anxiety, or even neurological problems.
There's a good (brief) article on it here -
http://www.usask.ca/wcvm/herdmed/applied-ethology/behaviourproblems/tailchase.html