Unfortunately, animals are personal property under the law, so all you are limited to is the vet bills and any diminished value of your pet, if applicable. You can not recover for pain and suffering/mental/emotional distress damages for loss of, or damage to, property for yourself or the dog. If the owners balk at the bills, sue them. You should also report this is a crime since it is against the law to have the dog unleashed like that. Also, make complaints to both Animal Control and the City both will open a file on the animal and if it has any complaints in the past, they will start a fining and hearing process on the dog owners. There is one California decision from OC in which pet owners were allowed emotional distress damages, but it is for a very narrow premise and last I checked it was not law of the state.
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I'm sorry to hear about your situation. The following guide should contain helpful information:
You should consider discussing this case with a personal injury attorney. The owner of the rottweiler is liable for your dog's damages. Best of luck to you and your dog.
Your second response (the first being getting your dog treated, of course) should have been to file complaints with both the police and Animal Control. You do not state whether you did that.
You should use this time to document any further incidents of the rottweiler being off-leash, particularly any attacks. Neighbors may be helpful.
When you have ascertained ALL your damages; vet costs, prescriptions, lost wages, etc., you can send a demand letter to the dog's owner(s). Should they fail to respond, you can sue them in Small Claims or retain counsel. Given the evolution of animal case law, retaining counsel would be beneficial.
The foregoing is for general information purposes and does not establish an attorney-client relationship.