 Lactation proceeds for 19 to 42 months, but calves, rarely, may suckle up to 13 years. Like other whales, the sperm whale's milk has a higher fat content than that of terrestrial mammals: about 36 %, compared to 4 % in cow milk. This gives it a consistency similar to cottage cheese, which prevents it from dissolving in the water before the calf can eat it. It has an energy content of roughly 3,840 kcal / kg, compared to just 640 kcal / kg in cow milk. Calves may be allowed to suckle from females other than their mothers.
