For survival reasons, birds are conditioned to sacrifice growth and reproduction when confronted with a pathogen or other stressor. In times of stress, this reacting mechanism prioritizes the allocation of resources to immune functions at the cost of performance. By reducing the impact of pathogens and the need for an inflammatory response, nutrients can be utilized for growth.
The formation of immunity in birds
The formation of the chick’s immune system begins during embryonic development, around days 3–4 of incubation. Around day 5, a chick embryo develops two important organs: the thymus, which produces T cells, and the bursa of Fabricius, which produces B cells. Both organs undergo rapid growth and development during the first few weeks of embryonic development.
Overall, the immune system of the chick embryo develops rapidly and is functional by the time the chick hatches. This early development is important for the survival of the chick, as it allows them to respond to infectious agents soon after hatching. Following hatching, the immune system of the chick continues to develop over the first weeks. From this point, there are two distinct types of immunity:
- Innate Immunity – The first defense line consists of different components like physical barriers (e.g. mucous membranes), as well as non-specific immune cells that react vigorously against any foreign materials, pathogens, or environmental stressors. Overstimulation of the innate immune system leads to inflammation as a natural response to infection.
- Acquired Immunity – Divided into two parts, effective and passive, this type of immunity is developed over a bird’s life as the result of encountering different diseases or vaccines.
Immunity threats on poultry farms
Poultry live in an environment full of microbes and environmental danger signals (Gallucci and Matzinger, 2001). Exposure to these pathogenic and non-pathogenic factors—through the air, water, and feed—can stimulate pattern recognition receptors (PRRs) including toll-like receptors (TLRs) that recognize molecular patterns present on the surface of various microbes like bacteria, viruses, and fungi. When a TLR recognizes a specific pattern, it initiates a signaling cascade that activates a transcription factor called NF-kB. A key player in the immune system, the activation of NF-kB leads to the expression of a wide range of genes involved in both canonical and alternative inflammation pathways. These pathways are a sequence of biological processes that arise in response to harmful stimuli, such as pathogens or tissue damage.
Upon activation, there is a release of inflammatory mediators and proinflammatory cytokines such as IL-1, IL-6, and TNF-α. These proinflammatory cytokines are signaling molecules produced by macrophages, dendritic cells, and other immune cells to play a key role in the inflammatory response. They help coordinate the immune response to infections, but if produced in excessive amounts, they can cause tissue damage and reduce the health of the animal.
The cost of inflammation
Inflammation is the most prevalent manifestation of host defense in reaction to alterations in tissue homeostasis (Medzhitov, 2008). However, this vital process often comes with high costs for the following reasons:
- Fever and anorexia can alter the birds’ metabolism, increasing protein turnover
- Elevated requirements of energy and protein for:
- Fueling the immune system, which can reduce the availability of nutrients for other physiological processes, such as growth or egg production
- Maintenance of damaged tissues by the effect of leukocyte recruitment and subsequent oxidative stress
Therefore, maintaining a balanced immune system—one that functions quickly and efficiently so an overreaction of the immune response is not necessary—is considered important to avoid negative impacts on poultry production.
MCFAs as anti-inflammatory compounds
For innate immunity, medium-chain fatty acids (MCFAs) have a range of beneficial effects on the body, including both antimicrobial and anti-inflammatory effects. The anti-inflammatory effect of MCFAs is thought to be related to their absorption and transport from the intestine, through the blood, and directly to the liver; where they are quickly oxidized and used as a source of energy. Compared to long-chain fatty acids, MCFAs have also been shown to reduce inflammation. Furthermore, MCFAs are known to lower the production of pro-inflammatory cytokines. By reducing the production of these cytokines, MCFAs can help to manage inflammation in the body.
This is aligned with research conducted by Agrimprove, where the production of pro-inflammatory cytokines in the small intestine and the blood were measured in response to the application of Aromabiotic® Poultry (Figures 2 & 3).
Effect of Aromabiotic® Poultry on pro-inflammatory cytokines in the jejunum
Effect of Aromabiotic® Poultry on pro-inflammatory cytokines in blood
In general, the application of Aromabiotic® Poultry showed a tendency to reduce the overall production of the proinflammatory cytokines IL-1, IL-6, IL-8, and TNF-α in the blood and jejunum. The lower presence of these cytokines can be beneficial for the health and welfare of broilers.
The role of MCFAs in improving adaptive immunity
Concerning acquired immunity, the use of short- and medium-chain fatty acids (SCFAs and MCFAs) has
been investigated as a potential strategy for improving poultry health and immunity, including a beneficial response to vaccinations.
C-Prove 80 is a commercial product that contains a high concentration of SCFAs and MCFAs. Some studies have indicated the effect of C-Prove 80 on infectious bursal disease (IBD) and Newcastle disease (NDV) titers in poultry. It was shown that when applying C-prove 80 in the drinking water of broilers during the first 10 days and between days 18–21, a significant increase in serum antibody titers against both IBD and NDV was achieved. The increase in titers indicates an enhanced immune response to the viruses (Figure 4).
Effect of C-prove 80 on viral antibodies titers
Additionally, it is suggested that a combination of MCFAs with SCFA can be associated with an increase in the development of the bursa of Fabricius (Nguyen, 2018). A larger bursa is responsible for better antibody production and higher protection (Ammar, 2008).
As chicks are hatched with a primitive immune system composed of innate immunity and passive immunity from the mother hen, the first 6 weeks of the bird’s life are considered important for the development of its adaptive immune system. Though it takes longer to fully mature, the adaptive immune system is more specific and targeted. However, until the adaptive immune system matures, young broilers are vulnerable to inflammation from an exaggerated innate immune response. This can lead to suboptimal performance due to increased expenses associated with immune functions. In this regard, the use of MCFAs as a dietary supplement (in feed or water) for poultry has the potential to support a balanced innate immune system and reduce the negative impacts of inflammation. Additionally, MCFAs can support the development of the adaptive immune system, which improves the flock’s overall health and reduces the need for antibiotics.
References are available upon request.