Males protect their harem from other males, and may go months without eating while doing this. Young sea lions are precocial. They are mobile within 30 minutes of birth. The cow's milk is 36% fat. Females reach sexual maturity at 5 years, and nurse their young for 6 months, much longer than seals. Females mate about 10 days after bearing young in the spring, but the resulting embryo stops growth at the blastocyst stage for some months while the female is nursing. After the pup is weaned, the blastocyst attaches to the uterus wall, a placenta develops, and a normal pregnancy begins.