1. If the sows return to the situation within 20 days after mating (18-19 days), it means that the breeding is too late. 2. If the sows return to love after 22 days of mating (23-24 days), the mating is too early. 3, if 21 days, 22 days, 23 days after mating return to love, indicating that the failure of mating, then you need to fully consider whether the sow has the condition, the quality of sperm is eligible and other issues. 4. If you return to love within 39-45 days after mating, it means that you missed the last estrus cycle and you need to check the method of detection. 5, if the return within 25-38 days after mating, outside the normal range. A sow who is pregnant but unable to conceive may be due to stress, moldy feed, too few eggs for pregnancy, or uterine infection. 6, if the sows return to love after 45 days after mating, outside the normal range. Sows who are pregnant but unable to conceive can think of miscarriage, moldy feed, disease, stress or fight. 7, if the return within 3-18 days, it may be: ovarian cysts, uterine infection, moldy feed disrupted the normal reproductive cycle. 8. Insemination rules for returning sows: (1) Examine vaginal secretions of sows or other abnormal behaviors that impede breeding. (2) If all of this is normal, instinct will occur once a standing estrus occurs. (3) Once again every 8-12 hours, only until the sow no longer receives back presses.