First, the energy to perform essential body functions like digestion, respiration, heart functions, brain functions, etc. (Resting Energy Requirements or RER), which can be calculated by multiplying the animals body weight in kilograms raised to the ? power by 70, for example, a 10kg (22lb) adult neutered dog of healthy weight needs RER = 70(10kg) 3/4 H 400 Calories/day.