55 days after the cows give birth, direct inspection should be conducted for the cows that have not been in estrus before. According to the cow B-ultrasound and direct inspection, corresponding treatment should be carried out: for cows with corpora lutea on the ovaries, PG should be injected intramuscularly immediately, and breeding should be carried out after estrus; for cows that have not been in estrus after injection of PG, PG should be injected intramuscularly again after an interval of 14 days, and breeding should be carried out after estrus;

Note: The estrus induction procedure is not allowed for the breeding cows that are ready to be mated. For the breeding cows that are ready to be mated with corpora lutea, PG 0.4 mg/time can be injected intramuscularly, and breeding should be carried out after estrus.

16-18 hours after the end of the "estrus induction procedure" treatment, all cows should be inseminated; it is strictly forbidden to touch the follicles before, during and after insemination, and the follicles can be observed by cow B-ultrasound; when normal estrus occurs during the "estrus induction procedure" treatment, breeding and insemination can be carried out, and the procedure treatment should be ended; when carrying out the "estrus induction procedure", the requirements of the procedure must be strictly followed.

Treatment of empty-stomach cows confirmed by pregnancy examination: rectal examination technology must be used to determine whether they are empty-stomach cows 60 days after mating: B-ultrasound examination technology for cattle must be used to determine whether they are empty-stomach cows 30 days after mating.

Cows with no corpus luteum confirmed by rectal examination and meeting the conditions of estrus induction procedure shall be treated according to procedure 2 (the number of days when the treatment is carried out shall be arranged according to the actual number of days);

Cows with corpus luteum and meeting the conditions of estrus induction procedure shall be treated according to the procedure (the number of days when the treatment is carried out shall be arranged according to the actual number of days);

Cows confirmed by B-ultrasound examination shall be treated according to the plan after intramuscular injection of PG; For cows that are ineffective in the "estrus induction procedure" plan, other plans can be used to induce estrus. Cows that are not pregnant 30 days after mating can repeat this plan once.