The digestive organs of sows over 4 months old have developed, and their digestive function and ability to adapt to the environment have gradually increased, which is the physiological maturity of internal organs development. Before the age of 4 months, the relative growth rate of gilts is the highest, and the bone growth rate is the fastest, and it gradually slows down after the age of 4 months. Muscle grows rapidly from 4 to 7 months, and fat begins to deposit in the body after 6 months. All fast-growing sows have strong reproductive ability, so good reproductive conditions should be given to reserve sows in the fastest growing period in order to obtain better adult weight and future reproductive performance. Therefore, it is necessary to observe the growth of sows regularly and make reasonable selection and elimination.