During a pig's estrus period, B-ultrasound observation of BCF imported pigs showed that the number of ovulations could reach 20-30, but it was more significantly affected by their breed or parity. The number of ovulations in sows reaching the initial estrus period gradually increased with age or the number of estrus periods, and gradually stabilized around the fifth estrus period; In addition, it is also affected by temperature changes. When the temperature is within the appropriate range (10-25 ℃), the number of ovulation increases, otherwise it decreases; Through B-ultrasound observation of pigs, it was found that the ovulation rate of sows is not significantly affected by nutritional levels. Postpartum sows are in a tight production state all year round, and the reserve sows for the first mating are still in the stage of production and development. Therefore, it is particularly important to pay attention to protein supply. The protein level in the diet depends on the type and content of essential amino acids. If protein is insufficient or has low biological value, it will not only affect the development of sow eggs, reduce ovulation, but also reduce conception rate and litter size. The energy level in the diet should also be taken into account. For thin and weak sows, the energy level should be appropriately increased.

Insufficient intake of vitamin A can lead to decreased sexual function, affecting follicular maturation and implantation of fertilized eggs; Insufficient intake of vitamin D can affect the absorption of calcium and phosphorus, leading to metabolic disorders; Insufficient intake of vitamin E can lead to infertility. When using pigs for B-ultrasound observation, it can be found that the ovaries of sows are sometimes in a quiescent state. During this period, it is advisable to provide an appropriate amount of green and juicy feed, which has a good impact on ovulation and fertilization. Feeding sows for the first time 10-14 days before mating can increase ovulation count. The ovulation rate of sows that freely feed during lactation is higher than that of first born sows that implement feeding restriction on the nipple for 21 days or the last 7 days, due to follicle growth during lactation. This will affect the number of ovulation in the future.