Surprisingly, yes. Too much protein can damage the kidneys. The horse's kidney system is designed to filter blood so that waste products are removed from the body. The kidneys function by filtering out waste products and reabsorbing water from the urine. In healthy horses, the kidneys work well enough to keep the water balance within normal limits. The amount of water a horse needs is determined by the horse's size. Small horses need about 2 gallons (8 liters) of water per day; larger horses need about 4 gallons (16 liters) per day. Horses need to drink about 3 cups (80 ml) of water per day for each pound (0.5 kg) of body weight. The water is used to remove waste products and excess salts from the horse's system. The waste products are then eliminated in the urine.