Immunomodulators in Poultry: Tool for Immune Optimization and Profitable Poultry Production.

In the dynamic landscape of poultry production, maintaining optimal immune function in poultry is critical for health, performance, and profitability. Immunosuppression, vaccine failures, and emerging pathogens continue to threaten productivity and profitability. With increasing pressure to reduce antibiotic use, improve disease resistance, increase vaccine efficacy, and support overall flock health, immunomodulators have emerged as a promising tool.  Understanding avian immunology and leveraging effective immunomodulation strategy has become more important than ever.

Basic Avian Immunology

The immune system in poultry is a complex and dynamic defence network that protects against pathogens while supporting growth and productivity.

Birds possess a complex immune system composed of innate and adaptive components. The innate immune system provides immediate, non-specific defence through physical barriers, phagocytic cells (like macrophages and heterophils), and soluble factors. The adaptive immune system, which develops over time, includes B-cells (producing antibodies) and T-cells (mediating cellular immunity), maturing in the Bursa of Fabricius and thymus, respectively.

Key immunity challenges in Broilers

Poultry have relatively underdeveloped immune system at hatch which makes early-life   immunity development critical. With a short lifespan of 35–45 days, broilers rely heavily on maternal antibodies and early vaccination. Rapid muscle development can divert nutrients away from immune development, increasing susceptibility to disease. Also environmental, nutritional, and management stressors can quickly suppress immune function in broilers.

Environmental stressors such as high ambient temperatures, poor ventilation, and fluctuating humidity levels are common in poultry houses, especially during summer and monsoon seasons. These stressors impair immune responses and increase susceptibility to infections.

High pathogen load such as Infectious Bursal Disease (IBD), Newcastle Disease (ND), Chicken Anaemia Virus (CAV), Inclusion Body Hepatitis (IBH), Reo Virus and Low Pathogenic Avian Influenza (LPAI) remain prevalent and continues to cause immunosuppression even in vaccinated flocks. Additionally, parasitic infections like coccidiosis and bacterial infections can become more prevalent when the immune system is supressed.

Key immunity challenges in Layers & Breeders

Layers face long-term exposure to pathogens such as viral, bacterial, and parasitic infections over their lifespan. Stress from production cycles, peak laying periods, molting, and feed changes can suppress immunity.

Respiratory Diseases such as Mycoplasma gallisepticum, Infectious Bronchitis, and Infectious laryngotracheitis (ILT) are common in layers. Newcastle Disease, LPAI are also major threats for optimum layer bird productivity.  Limited mobility and high density can elevate stress hormones, reducing immune responsiveness. Inadequate levels of vitamins (A, E, D3) and trace minerals (Zn, Se) impair immune function and vaccine response.

Broiler breeders encounter dual stress of growth and reproduction. Balancing body weight and reproductive performance can strain immune resources. In case of breeders, there is a potential risk of vertical disease transmission like Salmonella, Mycoplasma, and Avian Reovirus from parents to progeny. Breeders receive extensive vaccination schedules, which can cause temporary immunosuppression if not managed properly. High mycotoxin levels in the feed can affects egg quality, antibody production, and maternal antibody transfer.

Other important factors contributing to lower immunity in Broiler, Breeders & Layers

Mycotoxin contamination in feed is a silent but significant contributor to immunosuppression in broilers. In tropical and subtropical climates, feed ingredients are highly susceptible to contamination, especially with aflatoxins, ochratoxins, fumonosins, deoxynivalenol (DON), and zearalenone (ZEA). Even at subclinical levels, these toxins can significantly impair the immune system of broilers.

Mycotoxins can have several impacts on different organs which impact immunity.  

• Upon ingestion, the intestinal epithelium can be damaged, increasing intestinal permeability and therefore opportunity for bacterial infections.
• Lymphoid organs like the Bursa of Fabricius, thymus, and spleen can atrophy which reduce development of B- and T-lymphocytes compromising both humoral and cell-mediated immunity.
• Phagocytic activity of macrophages and heterophils can also be suppressed leading to reduced production of cytokines and interferons, weakening the first line of defence by impairing innate immunity.
• The liver is affected which can reduce the ability to produce acute phase proteins, an important aspect of innate immunity.

Because of these impacts due to mycotoxins, the response to vaccines can be impaired mainly in the production of antibody titers post-vaccination (e.g., ND, IBD). Antigen presentation is a key step in the production of antibodies and memory immune response which can be impacted by mycotoxins. Mycotoxins induce reactive oxygen species (ROS), damaging immune cells and tissues.

Other considerations for poor immune status are:

• Depletion of antioxidants like vitamin E and selenium
• Heat stress condition increasing corticosterone levels suppresses lymphocyte proliferation and antibody production; oxidative stress can be increased which can cause cellular damage if left unchecked
• Poor ventilation leads to an accumulation of ammonia, carbon dioxide, and dust particles. Ammonia damages the respiratory epithelium, impairing mucosal immunity. Chronic exposure reduces macrophage activity and increases inflammation.
• High humidity promotes pathogen proliferation and mycotoxin production in litter and feed. Low humidity dries out mucosal surfaces, reducing barrier protection.

Summary: Impact of Low Immunity in Poultry

Poultry Type	Key Impacts of Low Immunity
Broilers	– Increased disease outbreaks (e.g., IBD, coccidiosis) – Poor vaccine response – Reduced growth rate and FCR – Higher mortality and medication costs
Layers	– Chronic infections affecting egg production – Poor shell quality and egg hygiene – Increased culling due to disease – Long-term productivity loss
Broiler Breeders	– Reduced fertility and hatchability – Poor maternal antibody transfer to chicks – Higher risk of vertical disease transmission – Reproductive and systemic health issues

Holistic approach to overcome immunity challenges in poultry

• Biosecurity: Strict hygiene, controlled farm access, and disinfection protocols.
• Nutrition: Use of immunomodulators, probiotics, and mycotoxin mitigation strategies to support gut health and immune function.
• Monitoring: Regular serological and performance monitoring to assess vaccine response and flock health.
• Mycotoxin Management: Regular feed testing and use of broad-spectrum toxin binders. Critical for all poultry types to prevent immunosuppression and gut damage.
• Vaccination strategy: Broilers: Early-life vaccination with proper timing and handling. Layers & Breeders: Comprehensive vaccination schedules with booster doses and serological monitoring
• Stress Reduction: Minimize handling, overcrowding, and transport stress. Reduce heat and cold stress to prevent immune suppression.

The use of immunomodulators in poultry feed and drinking water has become increasingly popular as a way to address issues related to low immunity. 

What Are Immunomodulators?

Immunomodulators are substances—natural or synthetic—that modify the immune response. In poultry, they can either stimulate (immunostimulants) or suppress (immunosuppressants) immune activity, depending on the desired outcome. The goal in poultry production is to enhance immune competence without triggering chronic inflammation or metabolic stress.

Lysozymes, oligosaccharides, probiotics and prebiotics, phytochemicals, herbal extracts, beta-glucans and polysaccharides, vitamins and trace minerals, yeast cell wall components are some of the examples of immunomodulators used in poultry.

Mechanisms of Action

Immunomodulators work through multiple pathways:

• Enhancing innate immunity: Stimulating macrophages, heterophils, and natural killer cells.
• Boosting adaptive immunity: Improving antibody production and T-cell responses.
• Modulating gut microbiota: Supporting a healthy gut environment, which is closely linked to systemic immunity.
• Reducing oxidative stress: Antioxidants protect immune cells from damage during infections or vaccination.

Lysozymes are antibacterial enzymes that produce immunostimulant effect. They can cleave peptidoglycans of bacterial cell walls producing peptidoglycan fragments which are recognized by antigen presenting cells (i.e. macrophages and dendritic cells) which can have a priming effect allowing for greater immune activation which can be especially helpful for vaccination response. Lysozymes can also form pores within bacterial cell walls due to their cationic nature causing osmotic imbalance and eventual death.

Depending on the oligosaccharide, it can either be a food force for bacteria or can be a signalling molecule for specific pathways of the microbiome. This can lead to an increase in bacterial population or diversity or a change in behaviour of the microbiome.

Plant extracts comprising number of active substances entail adaptogenic (antistress) and immunostimulant properties. Plant extracts stimulate cellular immunity through phagocytic activity of macrophages, lymphocytes genesis and T- cell activity. Several phytogenics also have antibacterial properties.

Vitamins and minerals are essential for several biochemical reactions within the body as many of them are catalysts in enzymatic reactions necessary to keep proper physiological function. Some of them have additional functions like antioxidant properties (Zn, Se, Vitamin E) that are crucial for immune function.

Benefits of Immunomodulators in Poultry Production

The strategic use of immunomodulators offers several advantages:

• Improved vaccine response: Birds show higher antibody titers and better protection against diseases like ND, IBD, and IB.
• Reduced disease incidence: Enhanced resistance to bacterial, viral, and parasitic infections.
• Better growth performance: Healthier birds exhibit improved feed conversion ratio (FCR) and weight gain.
• Lower antibiotic usage: Supports antibiotic-free production by reducing the need for therapeutic interventions.

Table 1: Feed conversion ratio (FCR), Mortality rate, and geometric mean haemagglutination inhibition (GMHI) titres against Newcastle disease vaccine (A. Qayyum et al., The Journal of Animal & Plant Sciences, 22(1): 2012, Page: 11-14)

ISSN: 1018-7081

	Performance on day 42		GMHI titres days after Vaccination
Groups	FCR	Mortality %	3	13	23
Control	1.9	29.97c	7.29a	33.51a	12.69a
Lisovit® (100 mg/kg BW)	1.85	13.3b	7.99a	185b	84b
Lisovit® (200 mg/kg BW)	1.82	2.2a	8.00a	244c	140c

Table 2: Feed conversion ratio (FCR), Mortality rate, and geometric mean indirect  haemagglutination  (GMIHA) titres against infectious bursal disease vaccine (A. Qayyum et al., The Journal of Animal & Plant Sciences, 22(1): 2012, Page: 11-14)

	Performance on day 42		GMIHA titres days after Vaccination
Groups	FCR	Mortality %	0	10	20
Control	1.9	29.97c	5.27a	35.09a	29.11a
Lisovit® (100 mg/kg BW)	1.85	13.3b	5.03a	255.19b	101.56b
Lisovit® (200 mg/kg BW)	1.82	2.2a	5.54a	387.01c	121.77c

(Note: The birds were vaccinated against ND on day 3 (intraocular) and day 18 (drinking water) of age by using Lasota strain and against IBD on day 8 (intraocular) and day 21 (drinking water) of age by using pathogenic strain. Group A served as control, while birds of groups B and C were offered Lisovit® at the dose rate of 100 and 200 mg/kg body weight (b.wt.), respectively on days 22, 24 and 26 of age.).

*Lisovit® contains lysozyme, immune stimulating herbal extracts and vitamins C and E.

Conclusion

The immunity challenges in broilers, layers, and breeders are multifactorial and dynamic. While vaccines remain essential, their success depends on proper implementation and integration with broader health management strategies. Immunomodulators role in enhancing immunity, reducing antibiotic dependence, and improving overall flock performance is becoming increasingly vital for healthier, more resilient birds.  Immunomodulators are not a replacement for good management, biosecurity, or vaccination—but they are a powerful complement. When used strategically, they help poultry producers meet the demands of modern farming, healthier birds, better performance, and more sustainable production.