Rearing is an important stage in pig production systems, where immunity plays a fundamental role.

Domestic animals during their lifetime face many challenges that their immune system controls. To achieve this, the immune system of animals has evolved throughout history to create mechanisms that allow them to defend themselves from aggressive agents in the environment. Therefore, animal immunity is classified into two main types: innate and acquired.

Types of immunity: innate and acquired

Innate immunity concerns all the processes, tissues, and molecules that animals possess in a permanent and general way to protect themselves against aggressive agents. With this type of immunity, animal organisms protect themselves against most potential aggressors, up to 90%. It is the first defense barrier of animals. Within this type of immunity, numerous examples are ranging from enzymes (in tears, saliva) to tissues (skin, nasal, and body hairs) and even cells (pulmonary or intestinal macrophages).

On the other hand, there is acquired immunity. This type of immunity is an achievement of evolution since it is constituted as the interaction of multiple animal defense processes. This type, in turn, is subdivided into some groups of acquired immunity.

1. Active immunity: this arises due to natural infection processes or through vaccination.
   1. Natural: there is a development of antibodies in the animal as a response to an infectious process.
   2. Artificial: the antibodies developed are generated by vaccination, where fragments of pathogens or the attenuated pathogen itself are inoculated into the animal. This process triggers a controlled immune response that ends with the formation of antibodies and the activation of memory cells for subsequent challenges.
2. Passive immunity: this immunity is obtained when animals receive antibodies from some external source. For this, there are two ways:
   1. Natural: the animal obtains the antibodies thanks to the immunity transferred by the mother during the lactation process. Colostrum is the first milk generated with a high load of antibodies that will protect the piglet during the weeks of the rearing stage.
   2. Artificial: occurs by the transfer of antibodies from a drug or transfusion.

Rearing stage in animals

The rearing stage in pigs is defined as the period of life between weaning and 50 kg of weight or approximately 70 days of life of the pigs. Therefore, it is considered a broad period where animals are faced with a myriad of challenges to their immune system.

When animals are born, they face the world and all the pathogens and dangers that this means. For piglets to protect against these challenges, sows provide them with immunity through colostrum. Colostrum is the first milk secreted by sows and carries a high load of antibodies. These antibodies have been developed by the mother during her life depending on the environmental challenges she has faced. Thanks to this, the antibodies transferred by the mother to piglets are special against pathogens that affect the farm or are in the region.

However, when the lactation period ends during breeding, this passive immunity begins to decrease. After the animals are weaned, the rearing stage begins.

Immunity in the rearing period

After lactation (weaning) ends, juvenile animals must strengthen their acquired immune system to cope with environmental pathogens on their own. In this way, they can develop their active immunity through natural challenges or the farm’s vaccination protocol.

This period is critical for pig farms. During the days that passive immunity begins to wane, there is a gap where the animals’ immunity is decreased. Between the decline of maternal antibodies and the development of self-antibodies, pathogens can colonize the animals’ systems and generate disease.

Commonly reported diseases in rearing pigs to include respiratory and digestive infections caused by Haemophilus parasuis, Haemophilus somnus, Pasteurella multocida, Bordetella bronchiseptica, Salmonella cholerasuis, Streptococcus suis, Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae, among others.

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Management in the swine rearing stage

For the pig rearing stage to meet performance standards, some management recommendations should be followed.

1. Reception and observation: when the piglets are weaned, they should be moved to the rearing area where the environment should be under their temperature and feeding needs. This is also the time to observe the animals and detect clinical signs of the locomotive (lameness), digestive (diarrhea), respiratory (cough), or nervous (hypothermia).
2. Classification and records: Pigs in the rearing area should be classified according to their weight, to ensure uniform batches and avoid stress problems. It is also convenient to start the corresponding records for each batch of animals regarding vaccination, weight controls, feed conversion rate, and feed consumption. On the other hand, during this stage, it is recommended to relocate the animals that have delayed growth concerning the other pigs.
3. Adaptation to the change of diet: between weaning and rearing, piglets go from milk to pelleted feed (feed). This change is stressful for the animals, and they may stop consuming feed. One strategy to avoid this is to hand feed weaned piglets with the mothers nearby; in this way, they will adapt to pellet consumption. On the other hand, specialized feed should be provided for this stage. It should be highly palatable and have the requirements for the rearing stage.
4. Water supply: a fresh and permanent water source should be available at weaning that is easy to consume. Piglets do not know how to drink as they were hydrated by milk, so water should be provided in easily accessible containers while they are adapting to drinking systems.
5. Observation of retarded piglets: Piglets that show growth retardation should be placed in a separate batch and the cause of that retardation should be analyzed. In addition, hand feeding, and supplementation should be provided to raise them uniformly.
6. Hygiene of the facilities: in the rearing stage there is a high susceptibility of piglets to multiple diseases due to the stress generated by so many changes (location, diet, groups). Therefore, it is when cleaning and hygiene measures should be maximized in this area.

Strategies to strengthen immunity during rearing

At this time, it is of great importance to strengthen the immunity of animals to prepare them for the challenges they will face.

1. Implement strict hygiene and disinfection protocols to reduce the load of environmental pathogens.
2. Improve nutrition schemes for animals in rearing, with more protein for their correct development.
3. Establish vaccination protocols according to the region and country to generate acquired immunity in rearing animals.
4. Include Good Livestock Practices and Good Biosecurity Practices in farm management.
5. Measure the quality of colostrum from sows to know the number of antibodies they transfer to piglets.
6. Separate animals that show signs of infectious diseases to avoid transmission to other animals.
7. Evaluate the most adequate moment for weaning, prioritizing their correct immunity and nutrition through lactation. Early weaning is associated with the susceptibility of animals to infectious diseases during growth.
8. Administer pronutrients natural immunostimulants, since they are molecules that strengthen the immune system of the animals during this stage. In this way, their defenses are reinforced, and the animals can overcome the rearing stage with better results.
9. Improve the palatability of the feed supplied: at the beginning of the rearing stage, when the animals are weaned, there can be an abrupt drop in feed consumption. This negative effect can be avoided by improving the palatability of the feed, stimulating its consumption. A product such as Alqueflav has flavors and aromas of natural origin that stimulate the appetite of pigs, and it is designed for the pig digestive system.

Conclusions

The immune system of animals has evolved during evolution to provide defense mechanisms against environmental threats. Therefore, two main types of immunity have developed: innate and acquired.

Innate immunity provides the first barrier of protection against challenges. Acquired immunity is a complex of specific defense mechanisms developed to confront pathogens. In this second type, the sow transfers antibodies to piglets through colostrum, protecting for a few weeks.

In the rearing stage, there is a critical period where the immunity of the animals decreases, and they must form their defense antibodies. Therefore, it is convenient to implement disease prevention measures and strengthen the immunity of the animals in this rearing stage.