Mother humpbacks can lose up to one-third their body weight when nursing. [VID: How much milk does a humpback whale calf drink in a day? Nursing calves drink about 50 gallons of milk per day. To keep this in perspective, health experts recommend adult humans drink a half-gallon of water every day. At 50% fat content -- five times that of human breast milk -- whale milk is incredibly nutritious. Humpback whales do not feed during the months they are on the breeding grounds. Thus, the mother produ