Females become fertile at about 9 years of age (the oldest recorded pregnant female was 14). Pregnancy lasts 14 to 16 months and one calf is born. Females give birth once every 4 to 20 years. Lactation lasts from 19 to 42 months, but calves can sometimes suckle up to 13 years.
Sperm whale milk has about 36 percent fat (cows’ milk has 4 percent) and has the consistency of cottage cheese, which prevents it from dissolving in water. The energy value of this milk is 3840 kcal/kg. Calves can also suckle from females other than the mother.
