The horse must have a USEF ID and a USDF Horse Identification (HID) number. The USEF ID is free and the USDF HID is $25.
Horses competing at USEF-licensed/USDF-recognized competitions must have horse registration with both organizations. For USEF, either a Horse ID, Annual or Lifetime Registration. For USDF, either a Horse Identification (HID) number or a USDF Lifetime Horse Registration (LHR).