Different breeding methods have a significant impact on the litter size of sows. B-ultrasound observation of pigs showed that the effect of artificial insemination in the first breeding of this cross was better than that of this cross and the first artificial insemination, and the effect of the second artificial insemination was better, and the number of litters was better than that of the latter two. The breeding method can increase the number of piglets by 0.1-0.6, and the number of live piglets per litter can also be increased by 0.2-0.63 piglets respectively compared with the latter two breeding methods. The main reason for the good effect of artificial insemination for the first breeding and artificial insemination for the first breeding is that the boar itself can be used to judge the best time for breeding the sow, which is of course the best. It uses pig B-ultrasound to identify the follicles of sows. In addition, due to the stimulation of the inbreeding, the sow will have the feeling of a boar crawling when artificial insemination is performed, which will cause less stress to the sow. The reason why artificial insemination is used for the first mating and the effect of re-mating with natural insemination is poor is mainly because the best mating time for the first artificial insemination is difficult to grasp. Although there are boar test estrus and observation by technicians and breeders, the effect is still not as good as the boar's own mating. Even many sows have missed the mating time when they are re-mated after the first worker insemination.

In production practice, the following three methods can also be used for mating, which can significantly increase the number of piglets:

① Repeated mating. That is, when the sow is in estrus and is suitable for insemination, the first insemination and mating are carried out, and the second insemination and mating are carried out after 12-18 hours. It is best to use pig B-ultrasound to identify its follicles before insemination.

② Double mating. During the timely insemination period, the semen of one boar is used for insemination and mating, and after an interval of 12 hours, the semen of another boar is used for insemination and mating;

③ Mixed semen insemination and mating, that is, the semen of two or more breeds of boars is mixed and diluted for insemination.

The results show that the best results for the conception rate and litter size of sows are achieved by double mating, followed by mixed semen insemination, because the former can increase the sexual excitement of sows, accelerate the maturation of follicles, increase the number of ovulations, and use pig B-ultrasound to check the size of follicles to determine whether they are mature. It shortens the ovulation time, giving the eggs a chance to choose sperm with strong vitality and affinity for fertilization, thereby increasing the conception rate. The latter gives the eggs more opportunities to choose sperm, thereby increasing the number of fertilized eggs, improving the conception rate and increasing the litter size.

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