A single calf is born after a gestation period of 15 months. Calves move freely by the end of their first day. Nursing and maternal care continue for one to two years. In a study to find whether young could exist on milk substitutes, two male, month-old camels were separated from their mothers and were fed on milk substitutes prepared commercially for lambs, and they grew to normal weights for male calves after 30 days. Lactational yield can vary with species, breed, individual, region, diet, management conditions and lactating stage. The largest quantity of milk is produced during the early period of lactation. The lactation period can vary between nine and eighteen months.