The horses received either intravenous ( IV ) romifidine ( loading dose : @gkg ( -@ ) ; infusion : @gkg ( -@ ) hour ( -@ ) ) ( treatment R , n = @ ) or romifidine combined with butorphanol ( romifidine loading : @gkg ( -@ ) ; infusion : @gkg ( -@ ) hour ( -@ ) , and butorphanol loading : @gkg ( -@ ) ; infusion : @gkg ( -@ ) hour ( -@ ) ) ( treatment RB , n = @ ) .