The main reason why primiparous sows are eliminated because they do not estrus is that the nutrition does not meet the growth needs of sow reproduction and self-development. There is a physiological need for sows, requiring the protein content in the body to reach at least 35 kg. Once this indicator is reached, the reproductive efficiency will be improved. veterinary B-ultrasound can play a very important role in this process. It is difficult to breed young sows after the first birth. One important reason is that the protein content is low, only 16-20 kg. It takes about 3-4 litters for the protein content in the body to reach the 35 kg indicator. Therefore, after the young sows are bred, they cannot be fed with high-nutrition feed according to the feeding requirements, and they must be fed in limited quantities to prevent the embryonic mortality rate from increasing. High-energy feed cannot be consumed in the middle and late stages of 30-105 days to prevent the negative effects of decreased feed intake during lactation. Priiparous sows have a low feed intake and are in the growth and development stage. Veterinary B-ultrasound is often used to detect back fat thickness to judge the feeding situation. This fails to meet the nutritional needs of primiparous sows, resulting in excessive weight loss after delivery. Some primiparous sows have many litters and good lactation performance. In order to meet the needs of lactation, the sows' body fat and body protein are used, resulting in excessive protein loss.

If the daily feed amount during lactation is insufficient, the sows will use the nutrients stored in their bodies to meet the needs of milk production, first using fat and then body protein. If the body protein loss during lactation exceeds 10% of the body protein content at delivery, the interval between weaning and estrus should be extended, and veterinary B-ultrasound examinations should be used frequently. The effect of fat loss in lactating sows on reproductive performance after weaning is not as close as that of protein. The feeding and management of sows should be low-energy feeding during pregnancy and high-energy feeding during lactation. After sows give birth, the daily feed amount should be increased to the maximum amount of nutritional needs as soon as possible, preferably within 7-10 days.