Lack of nutrition or sex hormones, non-estrus or infertility and management.

Feed long-term lack of vitamin A, D, E and minerals and trace elements, can cause sow oestrus normal and not ovulation. These substances should be added in time, the best way is to add sufficient vitamin A, D, E and minerals and trace elements, after 1 to 2 seasons, is expected to match the seed.

Progestin deficiency leads to early death of fertilized eggs due to lack of nutrition and non-implantation, mistaken for misregistration. The solution is to supply nutrition according to the above method, and on the seventh day after breeding, intramuscular injection of progesterone 20 to 30 mg.