What causes sows not to come into heat or to fail to conceive after repeated matings?

The first is inflammation of the reproductive tract (accounting for 70 to 80%), among which endometritis has a relatively high incidence. The second is a long-term lack of vitamin A, D, E, minerals and trace elements in the feed, which can cause sows to come into heat normally but not ovulate. The third is early embryonic death, caused by insufficient progesterone, which leads to a lack of nutrition for the fertilized egg and its inability to implant, resulting in early death, mistakenly thought to be a failure to conceive. The fourth is inbreeding, which can cause repeated failure to conceive. The fifth is abnormal structure of the reproductive organs, causing congenital infertility. The sixth is a temperature above 35 degrees, which reduces boar sperm motility and makes conception difficult.