 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 . 
