co-ownership of dog

I co -own a dog with a breeder. No contract was signed and the AKC papers are in my name and his. The dog had medical problems. Last infection was major and vet said spay the dog or you might lose her next time. Dog was spayed and now breeder wants to sue for dogs return and damages. Do I have to give back my dog? Can they sue for damages? What damages?

[annjd]

-If two or more owners or partners cannot agree on what to do with owned property such as a dog, they may petition the court and the court will order a sale or payment etc. so that the one or more may get out of the property and/or the other(s) may keep it etc.--it is often done-- (This is true in some cases even for equitable owners that have paid various amounts etc., but for various reasons, may not be listed as owner.

Thank you very much for the answer.