Sow gestation

Gestation is one of the most important stages of the sow’s reproductive cycle. Over approximately 115 days, embryos develop into piglets ready to be born.

Nutrition, health and stress management during this period all influence piglet size and vitality. Understanding how gestation progresses in sows provides a better insight into porcine reproduction and highlights the importance of caring for breeding females.

How long does gestation last?

Sow gestation lasts approximately 115 days, equivalent to three months, three weeks and three days.

During this period, significant biological changes take place in the sow, from the fertilization of the eggs to the growth and maturation of the fetuses. To better understand these changes, gestation can be divided into three main stages: embryonic development, fetal development and preparation for farrowing.

Fertilization and the beginning of gestation

Gestation begins with the fertilization of the eggs, which takes place in the reproductive tract following artificial insemination. Fertilization occurs when viable sperms are present at the appropriate time in relation to ovulation.

Following fertilization, the embryos begin to divide as they travel towards the uterus. During the first few days, they develop into blastocysts, which continue to develop and become distributed throughout the uterine horns.

Around days 11–14, key processes take place to establish pregnancy. The embryos produce signals that enable maternal recognition of pregnancy and begin to establish contact with the uterine tissue. This process is essential for gestation to continue.

The first few days of this stage are particularly delicate. It is therefore important to provide sows with appropriate nutrition, maintain suitable environmental conditions and avoid stressful situations that could compromise their welfare and the progression of gestation.

Embryonic development

During the first few weeks, the embryos develop progressively, forming the tissues and structures that will later give rise to their organs and body systems.

The placenta also develops during this stage, establishing the physiological connection between the sow and each fetus. Through the placenta, nutrients and other essential substances are transferred to support piglet development.

By around days 35–40, the embryos have progressed in the formation of their structures, and the fetal stage begins to take shape.

Not all embryos necessarily survive until birth. Embryonic losses can occur during the first few weeks and affect the final litter size.

Fetal development

Once the embryonic stage is complete, fetal development begins. The organs and tissues continue to develop, and the fetuses progressively increase in size.

Two periods can be distinguished during this stage:

• Early gestation: The development of organs, tissues and body structures continues.
• Late gestation: Fetal growth accelerates, and nutritional requirements increase significantly. The fetuses build up energy reserves and progress towards the level of maturity needed to adapt to life outside the uterus.

Development does not depend solely on the passage of time. Piglet growth is also influenced by factors such as the placenta’s ability to supply nutrients and oxygen, the sow’s body condition, nutrition, and other health and environmental factors.

For this reason, the sow’s diet should be adapted to her needs at each stage of gestation, following the farm’s technical recommendations.

Preparing for farrowing

As the end of gestation approaches, the fetuses complete their development and continue to build up energy reserves. At the same time, the sow’s body undergoes changes that prepare the reproductive tract and mammary glands for farrowing and lactation.

Signs that farrowing is approaching include an increase in mammary gland size, the appearance of milk secretion and behavioral changes, such as restlessness or nest-building behavior.

Monitoring sows during this period helps identify the onset of farrowing and organize the necessary care to support the sow’s welfare and piglet survival.

Pregnancy diagnosis and monitoring

Confirming pregnancy and carrying out appropriate monitoring are essential aspects of managing porcine reproduction.

During gestation, it is also important to understand the changes in the sow’s reproductive cycle. The absence of a return to oestrus is one indicator that may suggest pregnancy, although this must be confirmed using specific diagnostic methods.

There are several methods available to confirm whether a sow is pregnant. Ultrasound is one of the most widely used, as it allows structures associated with pregnancy to be detected and its progression to be assessed. Under suitable conditions, it can be used from approximately days 23–30, depending on the equipment, technique and operator’s experience.

In addition, monitoring reproductive records, observing the sows and tracking their body condition help identify potential issues and plan the next stages of the production cycle.

Sow gestation and its stages

Sow gestation is a complex process in which every stage plays an important role in the development and birth of future piglets. The care and management of the sow influence litter development and reproductive performance, from fertilization and embryo implantation to fetal maturation and farrowing.

Understanding how gestation progresses helps inform decisions about sow care and supports more efficient porcine reproduction, with particular attention to sow welfare and piglet viability.