Stevens says in a statement the probe will "examine organizational structures, internal communication and veterinary practices at all of the major components of Sheikh Mohammed's equestrian properties," which include extensive thoroughbred and endurance stables.
Stevens says he is appointing an inquiry team to work into 2014.
The inquiry was launched after Stevens met on Tuesday with International Equestrian Federation President Princess Haya of Jordan, who is the sheik's wife.
It could determine if FEI regulations were broken.
British authorities seized the shipment in May at Stansted airport near London.