A fundamental key in pig production is the pregnant sow. In this productive phase, there are key points for the farm to have optimal results. Here we will review the most outstanding aspects in the management of the pregnant sow.

Pig production

Pork is one of the main producers of red meat representing 40% worldwide. It is also important to highlight that pig is a domestic species with great adaptation to any system or installation. Among the production animals, perhaps the most notorious feature of the pig is its ability to be prolific. Litters of sows can range from 6-8 piglets per delivery in low and medium-scale production systems, to even 14-16 piglets per litter in highly technified production systems.

Sexual cycle of the sow

The sow is an animal whose sexual cycle is polyestric and, in the tropics, has sexual activity throughout the year. The estrous cycle of the sow lasts 21 days (15-28).

The estrous cycle phases are divided into:

• Proestrus: this stage lasts two days. Signs that may be seen include riding among females, red vulva, and secretions. However, at this stage, the sows do not yet accept the male. In proestrus the production of estrogen increases which prepares the sexual organs for estrous.
• Estrous: This stage lasts from 2 to 3 days. Signs that may be seen include inflammation of the vulva, vaginal mucous secretions, grunting, and vocalizations, decreased food intake, aggression. The most characteristic sign of estrus is the immobility reflex in which it is possible to mount or perform artificial insemination. After 26 to 40 hours of heat, ovulation will occur.
• Metestrus: This stage lasts about seven days. In the metestrus, progesterone production begins and, the corpus luteum appears.
• Diestrus: this stage lasts nine days. In the diestrus, high amounts of progesterone are produced. If fertilization is not achieved, the corpus luteum will regress, which will decrease progesterone. At the same time, new follicles will mature, and the estrous cycle will restart.

On the other hand, Quiles and Hevia (2005) found that light has an impact on the duration of the heat. It was reported that there is a higher incidence of heat in the morning, both in adult and juvenile sows. Besides, Cintra et al., (2006) found that heat can affect the duration of the cycle: the higher the temperature the estrus can last less.

All these aspects of the estrous cycle of the sow should be taken into account because they are the mainstay of pig farming. Besides, the correct handling and understanding of these phases by the producer improves the performance and management of the sows. If the stray cycle of the empty sow is handled correctly and the insemination or mounting is carried out at the appropriate time, the sow will get pregnant.

Diagnosis of gestation in the sow

The gestation of the sow has an average duration of 115 days, with a range from 112 to 120 days. The formula to remember this duration is 3 months, 3 weeks, and 3 days. The variation of gestation in the sow lies in environmental, management, reproductive, nutritional, and other factors.

To make the diagnosis of gestation, several methods are carried out in farms:

No return to estrus

After the sow has been artificially inseminated or mounted by the boar, the gestation should be monitored. One way is to check at 18-25 days post-insemination if the sow has signs of heat (estrus) again. Mainly the stillness reflex or the also called the lordosis test is re-evaluated. If the test is positive, it means that the sow did not get pregnant and went into heat again. The management consists of inseminating again. The advantage of this method is that the test does not require any specialized equipment and is easy to perform in field conditions.

Vaginal biopsy

The vaginal biopsy is reported to have between 90% and 100% reliability for the diagnosis of pregnancy and 75% for the detection of empty females. A vaginal biopsy consists of assessing under a microscope the cell layers that make up the vaginal epithelium, as well as the shape and structure of the cells in the strata.

Ultrasonography (ultrasound)

Ultrasonography is one of the most widely used diagnostic methods in porcine reproduction to evaluate the gestation of sows. In addition to confirming or discarding gestation, it allows counting the number of piglets expected in childbirth. Reproductive ultrasonography is recommended to be performed at day 35 of gestation, which is the time when the embryo becomes a fetus. Once the fetus has been consolidated in this period, it begins its process of bone formation where ultrasonography becomes important. The equipment provides images compatible with the bones of the piglets which allows to check its health status.

Repeating sows

There are sows that after being inseminated or mounted may not get pregnant. These types of sows require a second or third service. Repeat sows reflect how fertile pig production is in the farm. It is important to make a comprehensive diagnosis by the veterinarian to investigate the cause of these repetitions. There is a range of causes that generate the repetition of these sows that can be individual or environmental. Some of the most important are an ill-balanced diet, stress factors, or inadequate management.

Facilities for the pregnant sow

Gestation area

Once the gestation has been confirmed in the sow, it is considered a pregnant sow and the management is different from other pig populations. Pregnant sows must be transferred to facilities called “gestation areas.” This consists of a corral where the sow will remain throughout its gestation until a week before childbirth. This transfer operation aims to give the sow more space and reduce the stress to which it may be exposed, as stress can affect pregnancy. On the other hand, the diet is adapted, and a gestation specialist monitors the process.

Maternity area

One week before the expected date of delivery, the sow moves from the gestation area to the maternity area. Before doing this, the sow must be re-evaluated. Once transferred it is recommended to do a general physical examination where it is evaluated: weight and body condition and measurement of dorsal fat before admission to the maternity area.

This allows the zootechnician to make an evaluation and formulation of the most appropriate and balanced diet for the sow and its lactation.

The sow in the maternity area is completely bathed with soap and water to remove all the organic matter in order to protect the health of the piglets. Once in this area, the sow will be ready for childbirth.

Feeding on the pregnant sow

The feeding of pregnant sows is one of the most important factors in pig farming. The feed should be differentiated for each sow and based on the analysis of the individual body condition to adjust the daily consumption.

Classification of body condition is done on a scale of 1 to 5:CC1: very thin bristle where the bones of the pelvis and spine are very evident

• CC2: the same bone points are identified, but not to the naked eye
• CC3: optimal condition, where bone reference points are not so clearly observed
• CC4 and CC5: they are scales for overweight and obese sows.

It is recommended that the pregnant sow is in CC3 and that the first two-thirds of the gestation (day 0 to 75) be fed with 3 to 3.5 Kg of balanced food. For the last third of gestation (last 45 days), it is recommended to increase the food to 4.5 to 5 Kg to promote fetal development. The balance of the diet must be made by a professional according to each individual and the productive system.

Conclusions

The gestating sow is the main axis of pig production. It is vital to establish good management of the pregnant sow to ensure optimal reproductive performance. The management includes components at the level of heat detection, facilities, pregnancy diagnosis, and biosecurity. The implementation of all the recommendations and good livestock practices in these stages improves the conditions for the pregnant sow.

References

• Cintra, M. F., García, L. P., Hernández, Y. S., & Pérez, M. S. (2006). Características reproductivas de la cerda. Influencia de algunos factores ambientales y nutricionales. REDVET. Revista Electrónica de Veterinaria, 7(1), 1-36.
• Quiles, A. y Hevia, M. La pubertad de la cerda: factores que la influencian. Departamento de Producción Animal. Facultad de Veterinaria. Universidad de Murcia. Campus de Espinardo. Disponible en: http://www.porcicultura.com/articulos/reproduccion/articulo.php?.htm
• Trujillo, M. E., Silva, R. H., Gutiérrez, O. (2019). Reproducción del cerdo: una visión práctica. Universidad Nacional Autónoma de México. Disponible en línea: http://papimes.fmvz.unam.mx/proyectos/reproduccion_cerdo/Reproduccion_Cerdo.pdf
• INTA, s.f. Buenas prácticas de manejo en las distintas etapas productivas. Gobierno de Argentina. Disponible en: https://inta.gob.ar/sites/default/files/script-tmp-inta_porcinos_capvi.pdf
• Padilla Pérez, M. (2007). Manual de porcicultura.