In the future, the pig industry will definitely develop in the direction of process and factory, so batch production has become the best choice for pig farms. Batch production is currently divided into simplified batch production and precision batch production, and precision batch production is more suitable for the development of the mainland pig industry, and experts and scholars in various countries are also studying precision batch production.
The core technology of precision batch production is to regulate the synchronization of sow cycle, follicle development, breeding synchronization and delivery synchronization, and the relatively accurate grasp of sow estrus, mating and delivery timing is the key to success.
At present, the cutting-edge technology of batch production is also based on these 4 synchronous regulations, and then I will expound on the current cutting-edge technology related to batch production.
1.1. Gilts
Due to the random distribution of estrus time between gilts, it is necessary to feed alleprogesterone (14-18 days) to form an artificial luteal phase to achieve the synchronization of the sow sex cycle, 42 hours after stopping alleloproteges, PMSG injection can promote follicle development synchronization, and GnRH injection after 80 hours can promote ovulation synchronization of gilts [1].
Chen Xiaoyu et al. have found that the initial state of the ovaries has an important impact on the treatment effect of the timing of the sperm procedure, when the gilt ovary is in the luteal stage, the effect of the timing infusion procedure is the best, and when it is in the static estrus period, the timing of the spermation treatment will have a negative impact on the development of the gilt follicle and synchronous ovulation and reproductive performance [2].
Studies have shown that pig farms should avoid the sow estrus period when performing the scheduled insemination procedure, and can use PMSG for pretreatment before performing the scheduled insemination procedure to adjust the ovarian state of the gilts so that they are in the luteal phase, and then perform the timing infusion procedure, which is conducive to improving the batch production performance of the pig farm [3].
Jia Ruoxin et al. found that during the timed instilferization procedure for gilts, the inhibitor serum was replaced by PMSG to promote the synchronization of follicle development, and it was found that the number of surviving cell embryos, the number of blastocysts and the level of progesterone in plasma on the 23rd day of the scheduled sperm program were significantly higher than those in the PMSG and goat serum control groups, which showed that the inhibitor serum had a stronger effect on promoting follicle development than PMSG. It is expected to replace PMSG in the timed vas deferens procedure [4].
1.2. Sows are produced
High concentrations of prolactin during breastfeeding of sows can inhibit the secretion of GnRH in the hypothalamus, thereby inhibiting the sow's estrus, after weaning, the inhibitory effect of prolactin is relieved, the hypothalamus secretes GnRH and promotes the secretion of follicle-stimulating hormone and luteinizing-stimulating body by the pituitary gland, promoting follicle development. Therefore, periodic synchronization can be achieved by simultaneous weaning, with INJECTION OF PMSG in sows 24 h after weaning to promote synchrony development of follicles, and injection of GnRH after 56-72 h to promote synchronous ovulation[1].
2. Breeding synchronization
Synchronizing the sex cycle with follicle development can achieve sow breeding synchronization. The same batch of sows can achieve the same day of breeding, and the sows with long gestation periods can be induced to give birth at the same time, which can make the piglets uniform. Numerous studies have confirmed that it is feasible to synchronize breeding using timed sperm infusion techniques. In addition, a single timed insemination using OvuGel (a gel extended-release agent of the GnRH analogue) significantly shortened the herd delivery time frame and improved herd neatness [5]. Suárez-Usbeck A et al. found that after feeding gilts allopprogesin for 18 days, injecting 10 μg of busererillin at intervals of 120h and performing a timed sperm infusion at intervals of 30-33 h had no effect on sow reproductive performance, but it could make the birth piglets weigh more and the sows have a shorter duration of estrus, which is conducive to reducing the semen use of each sow, accelerating excellent gene exchange, and thus promoting the breeding process [6]. With the implementation of batch production, single timed sperm infusion and centralized delivery can help improve the survival rate of weaned piglets, which may become a future development trend [7]. However, if the ovulation time and ovulation concentration of sows are not well mastered, a single timed sperm is likely to cause a decrease in the birth rate and litter rate, so the application in the mainland is still limited. Wang Longyan et al. found that 200 μg of triprelin was replaced by 100 μg of gonamorelin during the timing of the fertilization procedure for the primary sow, and the results showed that tripprerine could improve the 7d disconnection rate of the first sow, and the follicle diameter reached the maximum on the 4th day of weaning and was higher than the follicle diameter of other groups, and the batch pregnancy rate was higher than that of the natural investigation and matching control group, indicating that the use of triprelin for scheduled infusion could improve the reproductive performance and utilization rate of the first sow [8].
3. Synchronization of childbirth
Delivery synchronization can be achieved by inducing delivery of sows at the end of pregnancy, a technique based on the birth mechanism that simulates hormonal changes at the start of labour, using exogenous hormones to artificially regulate the delivery process, so that sows can be concentrated at a predetermined period of time [9]. In general, due to differences in weaning, estrus duration and gestation period, the natural littering time range of the same batch of sows is about 10 days.
Through the simultaneous delivery treatment, batch production can achieve the effect of "all in, all out". In order to obtain a high piglet survival rate, it is necessary to strengthen the care of delivery during the same period of delivery to improve the batch production effect.
Contemporaneous delivery drugs are prostaglandins, prostaglandin analogues, or oxytocin [10]. Studies have shown that prostaglandin injection can make 92% of sows give birth on a working day [7], which is conducive to the care of piglets and cross-foster care of weak litters, reducing piglet mortality. Although there have been adverse reports of contemporaneous delivery, which is mainly related to the improper use of contemporaneous delivery drugs, prostaglandins and their analogues are generally injected no earlier than 2 days before the expected date of delivery, and premature injections often lead to low birth weight, prolonged delivery time, and increased stillbirths in piglets [7].
Prostaglandins are used to induce lutein lysis and oxytocin to enhance uterine contractions [10]. Combining the two can increase the effect of contemporaneous delivery. Kirkden et al. inject oxytocin 20-24 hours after injecting prostaglandins can quickly initiate delivery and increase the proportion of births during working hours [11]. However, other studies have shown that the use of oxytocin increases the proportion of sows having difficult births [12]. This may be related to the fact that the sow's cervix is not fully open when the oxytocin is injected.
Studies such as Kirkwood have shown that the combination of prostaglandins and oxytocin shortens the time to give birth to the first piglet compared with the use of prostaglandins alone, but it can cause sows to have difficult labor and increase the mean littering interval [13]. Therefore, sows should carefully choose oxytocin during simultaneous delivery. Studies over the past few years have shown that carbetocin is more durable than oxytocin and can be used as a safe and efficient alternative to oxytocin. Injection of carbetocin 24 hours after injection of chloroprostaglandin can quickly start delivery and reduce the interval between births. Therefore, carbetocin is likely to be a promising alternative to oxytocin.
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