How to improve piglet immunity in the farrowing unit

17 November 2022

Infectious diseases are one of the leading causes of piglet mortality in the farrowing unit. Due to the epitheliochorial placentation of swine, piglets cannot obtain immunity in the womb. Furthermore, piglets are born with immature immune systems that are unable to mount a response against the infectious challenges they face in the farrowing unit and in the nursery.

Piglets can obtain antibodies from colostrum, through a process called ‘passive immunity transfer’. For this reason, colostrum is vital to reduce piglet mortality. However, smart farmers can also put the odds in their favour by managing sow immunisation, which indirectly improves piglet immunity. Furthermore, farmers can gain another edge against infectious diseases in the farrowing unit by boosting piglets’ innate immunity with supplementation, prophylaxis, and by promoting a healthy gut microbiome.

Piglet immune system

The immune system of mammals can be divided into two sub-systems: non-specific immunity (also called innate or non-adaptive immunity) and specific immunity (known also as adaptive or acquired immunity). More than the nomenclature, it is important to understand the principles behind the immunity conferring mechanisms of the organism.

The most basic form of innate immunity comprises those barriers, physical or chemical, that naturally prevent pathogens from infecting an animal. The skin, acid secretions in the stomach, and mucus are some of these barriers. Many dangerous pathogens have evolved strategies to bypass these mechanisms.

Non-specific immunity is called so because it refers to tissues that pertain to the immune system but that can protect against a wide variety of pathogens. Cells such as macrophages, neutrophils, natural killer cells (NK) and eosinophils attack any invading microorganisms through a process known as phagocytosis, where they ‘gulp up’ the threats and destroy them.

Specific (or adaptive) immunity is a complex system that includes humoral and cellular responses. Humoral immunity refers to antibodies that are synthesised to target specific antigens, which are parts of pathogens capable of inducing an immune response, often proteins expressed in the surface capsids of viruses and the cell walls of bacteria. Cellular responses involve, as the name implies, cells, mainly lymphocytes, which are further subdivided into B and T cells. B cells mainly produce antibodies, whereas T cells fulfil many functions, some of which are:

Inducing death (apoptosis) in virus-infected or cancerous cells
Releasing cytokines to attract and activate macrophages
Induce the proliferation and differentiation of immune cells

Cellular and humoral immunity work in tandem, so the division is somewhat artificial. The key takeaway is that the immune system has the ability to react to specific pathogens and mount responses that effectively neutralise or destroy the invading microorganism. Furthermore, the immune system has the ability to ‘remember’ pathogens it has already fought against, that way, a stronger (more specific) response can be mounted faster in subsequent exposures. If there were no specific responses and no immune memory, vaccines would make no sense!

Piglets are born with innate immunity, but their adaptive system is immature. For one, they have not been exposed to specific antigens in the womb. And even if they had, their immune tissues could not mount a sufficiently strong response. This is quite a predicament! Piglets are born into a hostile environment where germs abound, without the defences to fend them off. This is where colostrum comes in.

Through colostrum intake, piglets acquire specific antibodies, immune cells and other active substances from the sow. There is also evidence that activated lymphocytes present in colostrum are conferred unto the piglet, and that these mount an effective cellular response for pathogens such as Mycoplasma hyopneumoniae (Brandrick et al., 2008). During the first days and weeks of life, when they are not fully immunocompetent, they are living on borrowed immunity. Without this gift from their dam, they would soon die. This should underscore the importance of colostrum intake, but also of other measures such as biosecurity; if piglets run out of maternally derived antibodies (MDA) due to a heavy pathogen burden, then they will get sick.

Another important point to keep in mind is MDA vaccine interference. When the sow is vaccinated pre-farrowing for diseases such as PCV2, it will transfer high levels of antibodies to the piglet and these could interfere with vaccine antigens. For this reason, piglets cannot be vaccinated outright; we must wait for maternal antibodies to wane.

For some other diseases, where breeding stock are not vaccinated, early vaccination is both sound and needed. A clear example of this is oedema disease, caused by shiga-like toxin producing E. coli, where piglets can be vaccinated as early as 4 days of age.

However, sow pre-farrowing vaccination is a crucial approach to managing the immunity of piglets. By actively immunising the sow, the hope is that those specific antibodies will be transferred to the piglet through colostrum. This is how we can protect piglets against many important diseases, such as the neonatal diarrhoea complex caused by E.coli, Clostridium perfringens, and others.

Piglet immunisation

To promote healthy piglets and reduce mortality, colostrum management is by far the best strategy. Adequate colostrum management begins well before farrowing because it largely depends on the health and immune state of the sow. You might want to read this in-depth discussion of colostrum management. Here is a summary of the top aspects to consider:

Sow body score at previous weaning: sows that lose too much weight during lactation will need more days to next farrowing, but they will also have inadequate colostrum production.
Gilt acclimatisation: replacement stock must be adequately acclimatised to common pathogens present in the farm, especially PRRSV.
Sow vaccination: sows must be vaccinated a few weeks before farrowing (depending on the vaccine) to produce colostrum with antibodies against the most important pathogens.
Stockmanship: stress in the days leading to farrowing can cause the colostrum to spill or production to be inadequate.
Farrowing unit management: heat stress is an important cause of hypogalactia and agalactia (lower or no milk production).
Sow nutrition: sows change their food intake before and after farrowing. The diet must be formulated to meet the demands of lactation.
Nesting behaviour: before farrowing, sows display behaviours that kickstart and reinforce a chain of hormonal changes. Farrowing pen design and —depending on the production system— providing nesting material facilitates colostrum and milk production.
Judicious use of oxytocin: while sometimes necessary, oxytocin has a negative effect on colostrum.

Piglets are born with permeable guts. This means that colostrum antibodies can pass from the gut to the bloodstream. However, this window of opportunity closes quickly. After 8 hours, gut permeability starts to dwindle dramatically. By 12 hours, it is about half. Complete gut closure can occur as early as 24 hours and, for practical purposes, one should assume only negligible amounts of antibodies can pass thereafter (Farmer et al., 2006). The bests farrowing unit managers make it a point of pride to get all piglets a stomach full of colostrum before 6 hours.

Piglets naturally crave colostrum, but they run into all sorts of trouble:

There are not enough teats available in very large litters
Heavier piglets prevent the runts from suckling (heterogeneous litters have this issue)
Some piglets are born too weak to feed on their own
Piglets become lethargic due to chilling
The sow did not produce colostrum
Dystocia (a difficult or prolonged farrowing, as well as stillbirths, are correlated with poor colostrum or reduced intake)
Sow death

Some of these issues can be corrected with good stockmanship; for example, drying piglets and providing an external heat source are easy ways to prevent chilling. There are also four important techniques to manage colostrum intake problems in the farrowing unit:

Split suckling: split piglets from heterogeneous or large litters into two groups, place one group in the heated creep area and allow the other to suckle. Alternate between groups.
Cross fostering: place ‘surplus’ piglets with another sow that has available teats. If possible, piglets should receive colostrum from their dam before cross fostering.
Teat training: guide weak and light piglets towards the teat, until a feeding rhythm is established.
Manual feeding: provide colostrum with a bottle. Cow colostrum can be used as a substitute. If there is no colostrum available, an energy mixture can be given with a syringe to promote that low-viability piglets feed on their own. Manual feeding is usually not financially sound in large farms.

A heated creep area prevents chilling but also allows for split suckling, one of the most powerful colostrum management techniques.

Even if colostrum intake is adequate, piglets remain susceptible to pathogens that don’t induce good immunity. Coccidia are the best example. To protect piglets, farmers must resort to metaphylactic treatments and supplementation.

Coccidiostats are an effective and safe method to protect piglets. Other preventive measures, such as supplementation with organic acids and probiotics, have received much attention lately. The underlying principle is to promote healthy gut bacteria. Gut microbiome plays a major role in immunity, especially against intestinal pathogens. For example, it is a well-established fact that Clostridia, dangerous toxin-producing bacteria, cannot proliferate in a gut rich with beneficial species. Gut ecology is complex and, even if we know the benefits of healthy gut microbiome, the specifics are still poorly understood.

Weaning is such a critical period because pigs’ immune system is not fully mature and yet they must face new disease challenges Stress in the transition to the weaner area can precipitate disease. Even if there are maternal antibodies still present, vaccination usually starts around the weaning period. The precise vaccination program depends on your area, and you should discuss it with your veterinarian, but at this stage pigs usually get their first circovirus shot and are immunised against Mycoplasma hyopneumoniae, the causative agent of porcine enzootic pneumonia. If used, Salmonella, PRRSV, and ileitis, are given around this time (3 weeks). A notable exception is where early vaccination is needed and works well, like in the case of oedema disease, which is caused by shigatoxin-producing E.coli. In these instances, piglets can be vaccinated as early as the first week of age.

Later, at around 6-8 weeks, they are immunised against other important pathogens, depending on disease situation.

As piglets move through the production process, maternally derived antibodies wane and their own adaptive immunity strengthens.

Farrowing pen pathogens

Piglets are born into a hostile environment where a host of pathogens attempt to get the best of them. The most important pathogens at the farrowing unit are those that cause scour, reproductive problems such as late-term abortions, and pneumonia.

Escherichia coli

E. coli is probably the most common pathogen in the farrowing unit. This bacteria causes watery diarrhoea that quickly leads to dehydration. Biosecurity and colostrum intake are the main methods to prevent and combat colibacillosis. Fortunately, sow vaccination is very effective to protect piglets through passive immunity transfer.
Sows are usually vaccinated a few weeks before farrowing.

Clostridium perfringens

C. perfringens type C is the causative agent of necrotising enteritis, which can quickly kill piglets. Clostridia are somewhat normal inhabitants of the gut, and they cause trouble when gut ecology is altered. Gorging, for example, promotes clostridial proliferation. Sometimes, it is the healthiest-looking piglets that die due to necrotising enteritis, to the befuddlement of farrowing-unit personnel. C. perfringens type A is considered an emerging pathogen that causes neonatal diarrhoea. This specific pathogen produces several types of toxins (Alpha and Beta 2) and causes a milder form of infection with lower mortality when compared to type C; however, it is much more prevalent nowadays.

Sow vaccination is crucial to prevent necrotising enteritis. Thankfully, it is highly effective, provided that colostrum intake is successful.

Rotavirus

A common cause of scour, rotavirus is practically universal in modern pig farming. Sows usually have good immunity against this virus, so correct colostrum intake should be sufficient. However, sow vaccination is effective for some types of rotaviruses, so you should consult with your veterinarian if immunisation would make sense in your context.

Because rotaviruses are so prevalent, some advocate for the ‘feedback’ technique, where sows are exposed to faeces from infected animals, with the hopes that they will produce antibodies and confer them to their piglets. Gilts especially should be acclimatised, that is, given sufficient exposure to circulating pathogens, so their colostrum contains anti-rotavirus antibodies.

Porcine Reproductive and Respiratory Syndrome virus (PRRSV)

PRRSV is one of the most important pathogens that affect pigs. This virus has several manifestations. In piglets and pigs of all ages, it can present as respiratory disease, causing losses all throughout the production process. However, the most devastating effects of PRRSV are felt in the farrowing pen. PRRSV can cause abortion, mummified foetuses, stillbirths, and, of particular significance to our discussion, agalactia.

One of the challenges posed by PRRSV is that it has a lot of genetic variabilities, so it is difficult to develop vaccines against it (Pileri & Mateu, 2016). At present, vaccination is one of the best strategies available to both prevent mortality in the farrowing unit and minimising losses in the later stages due to poor performance.

Porcine Circovirus type 2 (PCV2)

PCV-2 is a widespread pathogen that causes a complex of porcine circovirus diseases (PCVD) responsible for significant losses. Vaccination induces solid protective immunity and has been implemented in almost all swine herds worldwide. Piglets should be vaccinated as part of any immunisation programs and immunity management in the farrowing unit, due to the ubiquitous presence of the virus, and to protect grower-finisher pigs. Sow vaccination reduces the risks of PCV2-reproductive disease and early infections and should be performed depending on the status of the farm. You should discuss with your veterinarian what is right for your farm.

Coccidia

Coccidia are one-celled parasites that invade and destroy the gut lining, leaving the piglet malnourished –due to poor nutrient absorption– and susceptible to other infections, notably by C. perfringens type A.

Coccidia cause significant losses worldwide and are practically impossible to eliminate from the environment due to their method of reproduction. In addition, these parasites proliferate in the gut and produce enormous amounts of oocysts (Coccidia ‘eggs’) that pollute the environment.

While colostrum confers some protection, it is limited. Furthermore, there are no commercially available vaccines against this pathogen, so we can do nothing to strengthen passive immunity. Metaphylaxis with coccidiostats and biosecurity are the best approaches.

Importance of sow vaccination

What we can achieve through piglet active immunisation is very limited. Therefore, our efforts should centre around the sow and passive immunity transfer. Through sow vaccination, we can influence outcomes in the farrowing unit and beyond.

Sow vaccination programs depend largely on the challenges that the farm faces and on the region. However, with some exceptions, sows should be vaccinated against E. coli, C. perfringens types A and C, parvovirus and erysipelas. Although PRRSV and PCV2 vaccination should also be considered on positive and problematic farms. There are several transmissible gastroenteritis (TGE) vaccines available, however, it is not clear how effective they are preventing disease in piglets.

Sow immunisation protects piglets indirectly, through passive immunity transfer.

Impacts of active immunisation

Immunisation is one of the best methods at our disposal to prevent diseases in pig farming. We have very effective vaccines against some important pathogens of swine. Piglet immunity can be managed through sow pre-farrowing vaccination, colostrum management, and the active immunisation of piglets as soon as it is viable to do so.

To bring home the importance of immunisation through vaccines, we should remember that some of the biggest challenges and threats to the pig industry are diseases where we don’t have a vaccine, or where it provides variable protection: PRRSV, ileitis, and coccidiosis.

Every farm should decide which vaccines to use depending on several factors:

Cost/benefit analysis
Diseases prevalent in the region
Diseases prevalent on the farm
Local regulations

Tighter biosecurity, farrow-to-finish systems and all-in all-out management help to control pathogens and reduce the need to vaccinate in some situations. However, the context should always be taken into account. Normally, technified farms cannot afford not to vaccinate, as the risks of an outbreak are just too severe.

Importance of iron supplementation for piglets

We must not forget that the immune system is not limited to antibodies. Innate immunity, the gut microbiome, and non-specific immunity all play a role in keeping piglets healthy.

One of the greatest challenges of modern piglets is that, due to their fast growth rate, they quickly outgrow their iron reserves. Iron is an important component of haemoglobin, the protein in red blood cells responsible for oxygen transport.

Due to its unique chemical characteristics, iron is also involved in many other cellular interactions, including many pertaining to immunity. For example, neutrophils (a type of immune cell) kill bacteria through oxidation, but, without iron, the enzyme they use to produce oxidative compounds is inactivated (Cherayil, 2010).

Iron is also necessary for normal cell function. Iron-dependence is something shared by many life forms. In fact, one of the most curious mechanisms that the organism uses to fight bacteria is to deprive them of iron by keeping it inside the cells. For reasons that are not yet clear, lymphocyte differentiation is iron-dependent (Cherayil, 2010). This means that, without iron, lymphocytes get stuck in a stage of development. This impairs adaptive immunity.

Iron supplementation in piglets is, therefore, one of the most cost-effective ways to prevent piglet anaemia and to boost immunity.

References

Alexopoulos, J. G., Lines, D. S., Hallett, S., & Plush, K. J. (2018). A review of success factors for piglet fostering in lactation. Animals, 8(3), 38. https://doi.org/10.3390/ani8030038

Bandrick, M., Pieters, M., Pijoan, C., & Molitor, T. W. (2008). Passive transfer of maternal Mycoplasma hyopneumoniae-specific cellular immunity to piglets. Clinical and Vaccine Immunology, 15(3), 540-543. https://doi.org/10.1128/CVI.00466-07

Cabrera, R. A., Lin, X., Campbell, J. M., Moeser, A. J., & Odle, J. (2012). Influence of birth order, birth weight, colostrum and serum immunoglobulin G on neonatal piglet survival. Journal of Animal Science and Biotechnology, 3(1), 1-10. https://doi.org/10.1186/2049-1891-3-42

Cherayil B. J. (2010). Iron and immunity: immunological consequences of iron deficiency and overload. Archivum Immunologiae et Therapiae Experimentalis, 58(6), 407–415. https://doi.org/10.1007/s00005-010-0095-9

Declerck, I., Dewulf, J., Decaluwé, R., & Maes, D. (2016). Effects of energy supplementation to neonatal (very) low birth weight piglets on mortality, weaning weight, daily weight gain and colostrum intake. Livestock Science, 183, 48-53. https://doi.org/10.1016/j.livsci.2015.11.015

Declerck, I., Dewulf, J., Sarrazin, S., & Maes, D. (2016). Long-term effects of colostrum intake in piglet mortality and performance. Journal of Animal Science, 94(4), 1633-1643. https://doi.org/10.2527/jas.2015-9564

Declerck, I., Sarrazin, S., Dewulf, J., & Maes, D. (2017). Sow and piglet factors determining variation of colostrum intake between and within litters. Animal, 11(8), 1336-1343. https://doi.org/10.1017/S1751731117000131

Farmer, C., Devillers, N., Rooke, J. A., & Dividich, J. L. (2006). Colostrum production in swine: from the mammary glands to the piglets. Pig News and Information, 27(1).

Muns, R., Manteca, X., & Gasa, J. (2015). Effect of different management techniques to enhance colostrum intake on piglets’ growth and mortality. Animal Welfare, 24(2), 185-192.

Muns, R., Silva, C., Manteca, X., & Gasa, J. (2014). Effect of cross-fostering and oral supplementation with colostrums on performance of newborn piglets. Journal of animal science, 92(3), 1193-1199. https://doi.org/10.2527/jas.2013-6858

Opriessnig, T., Patterson, A. R., Madson, D. M., Pal, N., Ramamoorthy, S., Meng, X. J., & Halbur, P. G. (2010). Comparison of the effectiveness of passive (dam) versus active (piglet) immunization against porcine circovirus type 2 (PCV2) and impact of passively derived PCV2 vaccine-induced immunity on vaccination. Veterinary Microbiology, 142(3-4), 177-183. https://doi.org/10.1016/j.vetmic.2009.09.056

Pileri, E., & Mateu, E. (2016). Review on the transmission porcine reproductive and respiratory syndrome virus between pigs and farms and impact on vaccination. Veterinary Research, 47(1), 1-13. https://doi.org/10.1186/s13567-016-0391-4

Richard, O. K., Grahofer, A., Nathues, H., & Posthaus, H. (2019). Vaccination against Clostridium perfringens type C enteritis in pigs: a field study using an adapted vaccination scheme. Porcine Health Management, 5(1), 1-9. https://doi.org/10.1186/s40813-019-0127-8

Shin, S., Park, S. H., Park, J. H., Kim, S. M., & Lee, M. J. (2022). Age-Dependent Dynamics of Maternally Derived Antibodies (MDAs) and Understanding MDA-Mediated Immune Tolerance in Foot-and-Mouth Disease-Vaccinated Pigs. Vaccines, 10(5), 677.