In my experience there are no tax concessions/implications with racehorse ownership. It is considered a hobby for most. The tax dept. would not be so foolish to allow deductions for expenses as they know majority lose. My accountant is also a racehorse owner and I have never been able to claim anything. Not sure about types like Williams/Singleton etc, but it is a no win situation for govt. Lord knows it would boost interest in ownership ten-fold if it was considered investing.
They obviously consider share investing/speculating a more profitable exercise. Not sure why sometimes!