I don't know where you're located but you may want to look in to Stable Keeper Laws also may be known as agister laws, as you may actually have a case of owning the horses.
Im my state of Washington: Equine Legal Solutions - Boarding - Washington Law RCW 60.56.010
provides Washington persons and businesses with an automatic
lien on their customersí horses to satisfy debts incurred in caring for or providing services to those horses, such as boarding and training. This type of lien is sometimes called an agisterís lien, and it means the facility can refuse to allow a customerís horses to leave until the bill for those horses is paid in full.
Texas: Protecting Your Horse During a Dispute : Equine Law Blog
You're going to want to Google for your state, and the lien may not be automatic like they are here, but if the ammount you've spent care has not been recouped, you may very well have a couple of new horses.