Dysbacteriosis in Poultry: Impacts on Health and Productivity

Sonale Nagesh¹., Monika M² and Rokade J.J.³

¹Ph.D Scholar, ICAR-Indian Veterinary Research Institute, Bareilly, UP, 243122

²Scientist, ICAR-Indian Agricultural Research Institute, Hazaribagh, Jharkhand, 825405

³ Scientist, ICAR-Central Avian Research Institute, Bareilly, UP, 243122

Introduction

The health status of birds depends on the dietary intake of the birds, where feed ingredients solitarily constitute deciding factor in the cost of production in the poultry farming. The feed undergoes a complex digestive process in poultry, beginning in the crop where it is stored briefly and partially fermented by resident bacteria. It then moves to the proventriculus, where it is mixed with acid and pepsin, initiating protein breakdown. Next, the feed enters the gizzard, functioning as a grinding mill to reduce particle size. This grinding, combined with the action of acid and enzymes from the proventriculus, allows for the breakdown of proteins into smaller peptides. These peptides are further digested in the small intestine into amino acids, which are absorbed for the bird’s use. Carbohydrates and fats are also broken down in the small intestine for absorption. By the time the digesta reaches the ileum, the absorbable nutrients should be fully utilized, leaving only indigestible feed components. Though digestive system effectively maintains the digestion process of the birds, however, integrity of the gastrointestinal tract (GIT) and the intestinal microbiota of chickens, play vital roles in nutrition absorption, development of immunity, and disease resistance. The composition of microbiota can be influenced by many factors such as gut physiology, diet and environment. Recent research indicates that the gastrointestinal (GI) tract of a broiler chicken is colonized by approximately 640 bacterial species from 140 genera. The abundance and diversity of microbiota vary along the GI tract, with regions of harsher conditions and faster passage rates hosting fewer bacteria. It can also be put in this way, that the digestive tract of a newly hatched chicken is sterile, and colonization begins through environmental microbial contact. Also, accompanied by high rate of peristalsis motion at small intestine makes it less conducive for bacterial colonization, but it hosts high levels of Lactobacillus, which stabilize around two weeks of age. Most bacteria in the small intestine are facultative anaerobes, with Lactobacillus, Enterococcus and Escherichia coli comprising of 60-90% of total microbiota’s population. Other bacteria in the ileum and duodenum include obligate anaerobes such as Eubacteria, Clostridia, Propionibacterium and Fusobacteria. In early life, the caeca are dominated by Lactobacilli, Coliforms, and Enterococci, but due to slower peristaltic flow, a more stable and complex microbiota develops over time. By four weeks, the adult caecal flora, including Bacteroides, Eubacteria, Bifidobacteria, Lactobacilli, and Clostridia, were established.

Alterations in the GIT microbial community may have adverse effects on feed efficiency, productivity, and health of chickens. The microbiome refers to the totality of microorganisms associated with an organism. The microbiome has complex interactions with their hosts which could be harmful (pathogenic) or beneficial (symbiotic) and can play key roles in human and animal health. Villi, finger-like projections lining the small intestine, play a crucial role in nutrient absorption by increasing the surface area. The gastrointestinal tract’s complex microbes play a crucial role in gut health of poultry by aiding digestion, producing nutrients, protecting against pathogens, and contributing to the maturation of the host immune system. The small intestine of poultry typically harbors few bacteria, whereas the large intestine and caeca are teeming with billions of commensal bacteria, collectively known as the intestinal microbiome. This microbiome profoundly influences gut health and the overall well-being of the chicken host. One of its primary roles is to further digest and ferment feed, converting it into nutrients that can be absorbed by the intestines. Beyond this, the gut microbe plays a crucial role in immune system function. In newly hatched chicks, these bacteria stimulate intestinal tract development and prime the immune system. Once established, the microbiome acts as an immune defence system, preventing pathogenic bacterial colonization by occupying physical space, forming barriers on the intestinal wall, and producing antimicrobial peptides. Interestingly, recent studies have shown that a well-balanced microbiome can enhance nutrient absorption efficiency, improve feed conversion ratios, and even influence the behaviour and stress levels of poultry, highlighting its multifaceted importance in poultry health management. As many countries necessitated strict rules and regulations or banned the use of antibiotics as antibiotic growth promoters, rising need to find the sustainable alternatives or reduce the prevalence of bacterial diseases or enable good management practises with proper biosecurity measures for better production. With this background on the aspect’s knowledge of gut health, this chapter delves into the conditions of dysbacteriosis, exploring its causes, effects, and impact on poultry health and productivity. It concludes by outlining potential management practices to address these issues.

Dysbacteriosis

Dysbacteriosis = Dys (bad/difficult); bacteriosis = any bacterial disease

The term dysbacteriosis is used to describe a phenomenon where the healthy equilibrium of the gut flora is disrupted. Dysbacteriosis defined as the presence of a qualitatively and/or quantitatively abnormal microbiota in the proximal parts of the small intestine, inducing a cascade of reactions in the gastro-intestinal tract including reduced nutrient digestibility and impaired intestinal barrier function, increasing the risk of bacterial translocation and inflammatory responses (van der Klis & Lensing, 2007). Dysbacteriosis is associated with a decrease in microbial species richness and diversity in the caeca, with a rise in pathogenic bacteria like Escherichia coli penetrating deeper layers of the gut, especially in co-infected bird (Mohamed et. al., 2020). Dysbacteriosis (DB) is a poorly understood digestive condition in poultry that has increased in incidence following the EU-wide ban on the use of antimicrobials as growth promoters. Dysbacteriosis, can significantly impact poultry health and productivity. This condition leads to digestive disorders, resulting in poor nutrient absorption, reduced feed conversion efficiency, and slower growth rates, with affected birds often showing signs of malnutrition and weight loss. Additionally, dysbacteriosis can trigger intestinal inflammation, causing enteritis, diarrhea, reduced feed intake, and overall poor performance. The imbalance also weakens the immune system, making birds more susceptible to infections and diseases. Furthermore, a disrupted microbial balance increases the pathogen load, facilitating the colonization of harmful bacteria such as Salmonella and Clostridium perfringens, leading to diseases like necrotic enteritis. Consequently, overall productivity declines due to poor health, increased mortality rates, and higher costs associated with managing these adverse conditions. Understanding and managing dysbacteriosis is crucial for maintaining poultry health and optimizing growth and production efficiency. Apart from above conditions, dysbacteriosis conditions afftects the litter quality, where poultry farmers often notice a decrease in litter quality. Aside from being a risk factor for development of food pad dermatitis, poor gut health due to dysbacteriosis often leads to antibiotic use in broiler. Dysbacteriosis affects animal welfare and feed conversion efficiency, making prevention all the more important. Intestinal dysbiosis is an imbalance of the intestinal microbiota of multifactorial origin. The intestinal microbiota is the community of microorganisms that live naturally and balanced in the intestines of animals, and is composed of bacteria, archaea, fungi and protozoa, among others. In the case of broilers, dysbiosis can cause a series of problems such as diarrhoea, worsening growth parameters, increased mortality and greater susceptibility to different diseases. Dysbacteriosis and enteropathogens are the most common issues reported by veterinarians and technicians in poultry productions. These problems are the result of a reduction in the usage of growth promoting antibiotics (GPA), and consequently, an increased susceptibility of birds to present gastrointestinal tract (GIT) alterations. Understanding and managing dysbacteriosis is crucial for maintaining poultry health, optimizing growth, welfare condition and production efficiency of the birds.

Causes of dysbacteriosis condition in poultry:

1. Diet: Diet indeed plays a fundamental role in shaping intestinal bacterial populations. The gut microbiota, consisting of trillions of microbes, is highly influenced by dietary nutrients and metabolites, with diet being a major factor in modulating its composition and function(Yilian et al., 2023). Variations in feed composition, including raw materials and physical quality, can significantly impact the gut microbiota balance. There are serious health concerns, especially in the early phases of chick development, due to improper nutrition and unhygienic climate in GIT. Nutritional defects due to ration composition imbalances, grain accumulation, microbial load on feed affect gut health.
2. Stress and immuno suppression: These include handling, transport, overcrowding, and sudden changes in the environment. When birds experience stress, it can lead to a higher susceptibility to pathogenic bacteria. Stressful conditions can alter the intestinal environment, making it more conducive to the growth of harmful pathogens. This increased risk of pathogen growth can ultimately compromise the birds’ health and overall productivity. Maintaining optimal conditions and minimizing stress is essential for promoting a healthy gut and preventing disease in poultry.
3. Faulty brooding conditions: Optimal brooding conditions are crucial for the proper development of gut microbiota in poultry. Birds that receive the right brooding conditions develop a robust gut that can better handle the challenges encountered in a broiler shed. Early access to feed and water is vital, as the lack of digesta can lead to dysbacteriosis. In fact, the gut microbiota can undergo significant changes within hours if nutrients are absent. Additionally, water quality is essential to maintain normal intestinal function and the appropriate pH of the digesta. Ensuring these conditions helps promote a healthy gut and overall well-being in poultry.
4. Poor biosecurity:  Faulty biosecurity measures, particularly those related to clean-out and disinfection procedures, can have a detrimental impact on poultry health. When these procedures are not properly conducted, pathogens can be introduced into the poultry shed. This exposure to pathogens significantly affects gut health and development. Improper litter management practices have been shown to have a significant impact on the gastrointestinal tract (GIT) and microbiota of chickens. Studies have revealed that litter management can influence the microbial diversity in the air and birds’ respiratory systems, with distinct changes observed over time (Dinka et al., 2022). Effective biosecurity protocols, including thorough cleaning and disinfection, are essential to prevent the introduction of harmful pathogens and to support the healthy development of the poultry gut microbiome.

Key Infectious Agents Contributing to Dysbacteriosis in Poultry

1. Clostridium perfringens: This bacterium is a major contributor to dysbacteriosis in poultry, causing necrotic enteritis. Clostridium perfringens thrives in an anaerobic environment and produces toxins that damage the intestinal lining, leading to inflammation and necrosis. The toxins disrupt the gut’s normal microbial balance, reducing the population of beneficial bacteria and allowing pathogenic bacteria to proliferate. This imbalance compromises nutrient absorption and can result in poor growth rates, increased feed conversion ratios, and higher mortality rates.
2. Escherichia coli: E. coli is commonly found in the intestines of poultry and can become pathogenic under certain conditions. Pathogenic strains of E. coli, such as avian pathogenic E. coli (APEC), can cause colibacillosis, leading to severe intestinal inflammation. This inflammation disrupts the gut microbiota, promoting dysbacteriosis. The pathogenic E. coli strains outcompete beneficial bacteria, leading to an overgrowth of harmful microorganisms. This dysbiosis can result in diarrhea, poor nutrient absorption, and increased susceptibility to other infections.
3. Salmonella sps.: Salmonella infections are a significant concern in poultry production due to their zoonotic potential and impact on bird health. Salmonella can colonize the gut and disrupt the normal microbial community, leading to dysbacteriosis. The infection triggers an immune response, causing inflammation and damaging the intestinal epithelium. This damage alters the gut environment, favoring the growth of pathogenic bacteria over beneficial ones. Dysbacteriosis caused by Salmonella can result in diarrhea, weight loss, and increased mortality.
4. Campylobacter jejuni: Campylobacter is another important pathogen in poultry, often associated with foodborne illnesses in humans. In birds, Campylobacter jejuni can colonize the gut without causing overt clinical signs but can still disrupt the microbial balance. The presence of Campylobacter alters the gut microbiota composition, reducing the diversity of beneficial bacteria and promoting dysbacteriosis. (Jinji et al., 2023) This imbalance can impair gut health, leading to reduced nutrient absorption and overall poor performance in poultry.
5. Coccidia (Eimeria spp.): Coccidiosis, caused by various Eimeria species, is a parasitic infection that severely impacts the gut health of poultry. The parasites invade and damage the intestinal lining, causing lesions and inflammation. (Thabile et al., 2021) This damage disrupts the normal gut microbiota, leading to dysbacteriosis. The infection also weakens the bird’s immune system, making it more susceptible to secondary bacterial infections. Dysbacteriosis caused by coccidiosis can result in diarrhea, poor feed conversion, and reduced growth rates.
6. Avian Influenza Virus (AIV): Avian influenza can affect the respiratory and gastrointestinal tracts of poultry. The virus can disrupt the gut microbiota directly or indirectly through the immune response it triggers. The inflammation caused by avian influenza damages the intestinal lining, leading to an imbalance in the gut microbial community. This dysbacteriosis can exacerbate the severity of the disease, leading to higher morbidity and mortality rates.
7. Newcastle Disease Virus (NDV): Newcastle disease is a highly contagious viral infection that affects various systems in poultry, including the gastrointestinal tract. NDV can cause inflammation and damage to the intestinal lining, disrupting the normal microbial balance. The resulting dysbacteriosis can compromise nutrient absorption and overall gut health, making birds more susceptible to secondary infections and negatively impacting production performance.
8. Mycotoxin: Mycotoxins can affect the gastrointestinal microbiota both directly through their antimicrobial properties and indirectly by triggering the release of antimicrobial compounds from host cells damaged by mycotoxins. Numerous in vivo studies have explored how mycotoxins impact host microbiota (Guerre, 2020). Conversely, the microbiota can also alter the bioavailability of ingested mycotoxins and their metabolites. Mycotoxins, including aflatoxins, trichothecenes, zearalenone, fumonisin, and ochratoxin, can disrupt normal intestinal functions like barrier integrity and nutrient absorption. Certain mycotoxins, such as trichothecenes and ochratoxin, specifically impact the histomorphology of the intestine (Winnie et al., 2018).

Dysbiosis: Signs and Consequences of Imbalanced Gut Microbiota

Signs of dysbiosis in poultry may include changes in faecal consistency, such as diarrhoea or increased water content, along with a foul odour. Birds affected by dysbiosis may also exhibit reduced feed intake, poor growth rates, and increased susceptibility to diseases. These disruptions in gut microbiota balance can lead to impaired nutrient absorption, compromised immune function, and alterations in metabolic processes. Addressing dysbiosis in poultry requires a comprehensive approach, including dietary interventions, probiotic supplementation, and management practices aimed at restoring a healthy microbial community in the gut. It disrupts the gastrointestinal tract (GIT) environment, promoting the proliferation of pathogenic bacteria. These pathogens secrete toxins that enhance intestinal motility and induce changes in mucus quantity and composition. Additionally, dysbiosis leads to alterations in gastric acidity, decreased production of bacteriostatic peptides by the pancreas, and reduced secretion of immunoglobulin The syndrome typically manifests between 20 and 30 days of age. (Fabri, 2000; Wilson et al., 2005; De Gussem, 2007A (IgA).

Clinical signs include:

• Pale, glistening, or orange droppings with undigested feed particles
• Wet and greasy droppings leading to dirty feathers
• Occasionally foamy caecal droppings
• Reduced physical activity
• Increased water intake
• Decreased feed intake with a check in weight or reduced gain rates
• Increased feed conversion

• Thin, fragile, often translucent intestinal walls
• Watery or foamy intestinal contents
• Frequent presence of orange mucus and undigested particles in the intestines
• Ballooning of the gut
• Intestinal inflammation

Prevention of dysbacteriosis

• Implement an appropriate feeding program with a balanced diet containing all necessary nutrients for chicken growth and development.
• Use high-quality ingredients free of toxins, mycotoxins, and microorganisms, or implement control programs for these contaminants.
• Avoid ingredients or raw materials with high levels of anti-nutritional factors.
• Apply management measures to minimize stress, reduce density, and improve hygiene.
• Strengthen the intestinal epithelium and promote regeneration and functionality of its cells.
• Utilize natural solutions like pro-nutrients specifically designed to improve enterocyte function and physiology.
• Pro-nutrients stimulate specific genes in enterocytes, enhancing nutrient absorption surface and villi condition for improved feeding efficiency.
• Pro-nutrients make digestive mucosa more resistant to infections and prevent undigested feed presence, which can fuel pathogen growth.
• Pro-nutrients can replace antibiotic growth promoters, prevent microbial resistance development, as they act on cellular physiology rather than microorganisms directly.
• Quality of day-one-chicks
• Quality of drinking water
• Good coccidiosis control program
• Strict hygiene and biosafety
• Good ventilation, in order to reduce the risk of wet litter

Therapeutic management for dysbacteriosis

1. Probiotics: Introduce beneficial bacteria strains to restore microbial balance in the gut. Probiotics can compete with pathogenic bacteria for nutrients and space, thereby reducing their population and restoring a healthy gut environment.
   1. Prebiotics: Provide dietary fibers that serve as food for beneficial bacteria, promoting their growth and activity. Prebiotics help create a favourable environment for beneficial bacteria to thrive and outcompete harmful pathogens.
   1. Synbiotics: Combine probiotics and prebiotics to synergistically enhance their effects. This combination promotes the growth of beneficial bacteria introduced through probiotics while also providing the necessary nutrients for their proliferation.
   1. Dietary Modifications: Adjust the diet to include easily digestible nutrients and reduce anti-nutritional factors that may contribute to dysbiosis. This can involve using high-quality ingredients, avoiding contaminated feed, and ensuring a balanced diet for optimal gut health.
   1. Enzyme Supplementation: Supplement with enzymes that aid in the breakdown of complex nutrients, improving nutrient absorption and reducing the risk of undigested feed components that can promote pathogen growth.
   1. Immune Support: Enhance the immune system’s response to combat pathogenic bacteria by providing immune-boosting supplements or additives. This helps the bird’s natural defences to better handle and eliminate harmful microbes.
   1. Stress Reduction: Implement management practices to minimize stressors such as overcrowding, temperature fluctuations, and handling stress. Stress reduction can help improve gut health and reduce susceptibility to dysbiosis.
   1. Hygiene Management: Maintain strict hygiene protocols in the poultry environment to minimize the spread of pathogens. This includes regular cleaning and disinfection of facilities, equipment, and water sources to prevent microbial contamination.

Conclusion

Dysbacteriosis can have profound implications for the host, as acute dysbacteriosis may lead to the colonization of enteropathogenic microorganisms resulting in detrimental health effects. Pathogenic bacteria possess the capability to generate toxins and metabolites, thereby inducing heightened gut motility, increased gas production through fermentation, alterations in gut pH, mucosal irritation, inflammation, and escalated mucous secretion. Consequently, this cascade predisposes to diminished nutrient digestibility and absorption. Maintaining a harmonious equilibrium within the gut ecosystem stands as paramount in averting dysbacteriosis. Enhancing feed digestibility and integrating feed additives that modulate gut microflora serve as strategic approaches to uphold a more stabilized gut milieu, particularly in circumstances of intestinal stress, thereby forestalling dysbacteriosis. Effectively preventing and managing dysbacteriosis aids in advancing the economic viability of poultry enterprises through enhanced performance, health, and welfare standards, while concurrently reducing the prevalence of foodborne pathogens and mitigating the environmental footprint associated with poultry production.