Llamas were given each of four treatments intramuscularly with a @-week washout : TZ ( @ mg kg ( -@ ) ) combined with either morphine ( @ mg kg ( -@ ) ; M ) , xylazine ( @ mg kg ( -@ ) ; X ) , morphine ( @ mg kg ( -@ ) ) and xylazine ( @ mg kg ( -@ ) ) ( MX ) , or saline ( C ) .