The recovery by the owner of the injured dog may be reduced by the degree to which he or she was at fault. For example, if the attacking dog and the injured dog were running loose, the owner of the injured dog might be regarded as being 50% to blame for the incident. If the vet bill was $500, then the owner of the attacking dog would have to pay only $250.
In states that still have the "contributory negligence" doctrine, the owner of the attacking dog would have to pay nothing. These states include Alabama, Maryland, District of Columbia, North Carolina and Virginia.
To learn how the doctrine of comparative fault will affect your claim, whether you are the owner of the injured dog or the attacking dog, you should use the Liability Wizard that is part of the interactive book, When a Dog Is Injured Or Killed.