The heart and blood vessels contain approximately 9 U.S. gallons of blood in a 1000 lb horse (about 35 cc/lb) Giffin, James and Tom Gore, DVM.
The heart and blood vessels contain approximately 34 Litres of blood in a 450 Kg horse (9 U.S. gallons in a 1000 lb). Which equates to about 76 cc/kg (1.2 oz/lb) Giffin, James and Tom Gore, DVM.