Your dog is personal property just like, say, a car or a toaster.  Under the law it is known as a "chattel."  If you entrust your personal property with someone for a time being it is generally known as a bailment situation.  In a bailment situation the party who is entrusted with the personal property is under an obligation to keep the property intact and safe.  They are not permitted to sell or alter the property.  That would be known then as "conversion" where the person who is holding the property uses it as their own.  I think that you may have a case for the holding of the property and the refusal to return it.  For the spaying as well.  For the loss of future earnings, well, that may be tough - but not impossible - to prove.  What if she was not fertile and what if you did  not get as many puppies as you thought, etc. Good luck.