The gestation period of sows is (114 ± 4) days, which is divided into the early pregnancy, mid-pregnancy and late pregnancy. The early pregnancy is about 3 weeks, the mid-pregnancy is about 9 weeks, and the late pregnancy is about 1 month. The early pregnancy is the embryo implantation stage. Green feed or juicy feed should be fed more. The amount of compound feed should not be too much. Generally, 1.5-1.8 kg per pig per day is enough, and the amount of green feed should be larger. Pig B-ultrasound should be used for observation frequently; mid-pregnancy is the stage of breast development and fat adjustment, and 2.0-2.5 kg of compound feed should be fed every day; late pregnancy is the stage of rapid fetal growth. About 65% of the birth weight of piglets is increased in the late pregnancy. The nutrition required by sows is greatly increased, but the sow's feed intake is limited by the abdominal cavity volume, which is easy to cause insufficient nutrition supply. At this stage, pig B-ultrasound should be used to check the growth of the fetus. Therefore, high-standard feeding should be adopted in the late pregnancy. Generally, each sow is fed 3.5-4.0kg of compound feed per day to ensure nutritional supply, promote normal fetal development, reduce sow fat consumption, and accumulate nutrition for postpartum recovery and early lactation. Because primiparous sows are still in the growth and development period, they should be fed at a higher nutritional level throughout the pregnancy. Pig B-ultrasound detection shows that pregnant sows should ensure appropriate weight gain throughout the pregnancy period. Too little weight gain will affect postpartum lactation, and too much weight gain will cause stillbirth and poor appetite after delivery.

In the management of pregnant sows, it is important to determine whether the sow is pregnant as early as possible and accurately. Generally speaking, after the estrus sow is mated, if no re-estrus is found after an estrus cycle (about 3 weeks), it can be judged as pregnancy. Its external manifestations are fatigue, drowsiness, unwillingness to move, quiet behavior, steady actions, increased feed intake, increased body fat, shiny fur, and the vulva shrinking into a thin line. Large-scale pig farms basically use pig ultrasound pregnancy testers to accurately judge. The pig ultrasound test time is 30-80 days after mating. The pig ultrasound test site is 5 cm above the 1-2 nipples in the lower part of the sow's flank, and the probe points to the posterior rib of the opposite side, 45° from the horizontal. If the bladder is full, the uterus is filled with fluid, estrus or abortion, it is easy to cause misdiagnosis. Use pig ultrasound to repeat the test twice, and the accuracy rate is nearly 100%. In daily feeding management, it is necessary to avoid fighting, slipping and other mechanical injuries, so it is better to raise them in a single pen. In large-scale pig farms, limited pen feeding is generally used.

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