When recording a transaction, Ardex gives you the option to attribute that cost to a horse, or directly to an owner.
Note that an owner in Ardex can be an individual, or a business.
You can do this as either a Procedure, or via Transactions.
Open the Procedures window via the main menu
Click Client on the right
The Horse field will change to Client
Select the client to be charged
Select Client in the top-left
The Client field will activate, and prevent access to the Horse field;