The amount of blood in a cow is dependent upon the cow's weight; however, it is generally accepted that the blood volume of cattle is an average of 55 milliliters per kilogram. Smaller cows, such as calves, would have less blood than larger cows, such as bulls.
In older animals and obese animals, the amount of blood decreases from the amount of blood that was present when the animal was a healthy adult. The amount of specific components of blood, including plasma, can vary greatly from one species to another. Some components of blood may vary in volume based on the diet of the cow.