Ascites in poultry

Introduction

Ascites, commonly referred to as “Water Belly,” is a condition characterized by the accumulation of fluid in the abdominal cavity of broiler chickens. This disease is not caused by infection but rather results from a series of physiological events that lead to an imbalance in the oxygen supply to the body’s tissues. Ascites has become a major concern in the poultry industry due to its economic impact, with mortality rates reaching up to 25% in severe cases.

Why Are Broilers Prone to Ascites?

Modern broiler chickens are highly susceptible to ascites due to their rapid growth rate, high feed efficiency, and increased breast muscle mass, all of which contribute to a higher oxygen demand. The metabolic rate of these fast-growing birds is significantly high, and when the oxygen supply fails to meet this demand, ascites develops.

Causes of Ascites

Cause	Explanation
Rapid Growth Rate	Increased oxygen demand due to fast metabolism.
Poor Ventilation	Low oxygen levels and high carbon dioxide accumulation.
Cold Stress	Increases metabolic rate, leading to higher oxygen demand.
High-Energy Diets	Accelerates growth, placing stress on the heart and lungs.
Overcrowding	Causes oxygen depletion and increased stress levels.
Faulty Brooding	Improper brooding temperatures affect metabolic and oxygen needs.
Ammonia & Dust	Poor air quality impacts respiratory function.
Sodium Toxicity	High sodium levels contribute to fluid retention and circulatory issues.
Vitamin E/Selenium Deficiency	Leads to oxidative stress and weak cardiovascular health.
Mycotoxicosis	Toxins from moldy feed impair liver function and metabolism.
General Stress	Various stress factors exacerbate the condition.

Symptoms of Ascites

The clinical signs of ascites become more apparent as the disease progresses. These include:

• Sudden Death – Mortality rates peak between 35 and 42 days of age, though cases can appear as early as 15 days.
• Stunted Growth – Affected birds appear smaller and weaker and show reduced weight gain.
• Pale Head & Shrunken Comb – Due to poor blood circulation and oxygen deficiency.
• Labored Breathing – Birds may pant, struggle to move, or show visible respiratory distress.
• Abdominal Distension – In severe cases, birds develop visibly swollen abdomens due to fluid accumulation.

Diagnosis of Ascites

Ascites can be diagnosed based on clinical signs and confirmed through postmortem examination. Key postmortem findings include:

1. Distended Abdomen – Presence of excessive fluid in the abdominal cavity.
2. Clear Yellow Fluid Accumulation – Up to 300 ml of fluid, sometimes containing fibrin clots.
3. Enlarged Heart – Due to increased cardiovascular strain.
4.  Fluid collection around the heart.
5. Liver Abnormalities – The liver may be swollen, congested, or firm and shrunken.
6. Severe Lung & Intestinal Congestion, indicating respiratory distress.

Note: Some birds may die from ascites before fluid accumulation becomes noticeable, making early detection critical.

Treatment Options

Unfortunately, there is no highly effective treatment for ascites. However, certain measures can help reduce mortality:

1. Furosemide (Diuretic Medication) – Helps reduce fluid retention and alleviate symptoms.
2. Vitamin C, Vitamin E, and Organic Selenium – These antioxidants improve heart health and enhance resistance to oxidative stress.
3. Supportive Care – Ensuring proper ventilation and reducing stress can help affected birds cope better.

Prevention and Control Measures

Preventing ascites is far more effective than treating it. Poultry farmers can take the following steps to minimize the risk:

1. Controlled Feeding – Implement feed restriction or use lower-energy diets to slow excessive growth.
2. Adequate Ventilation – Maintain proper airflow to ensure sufficient oxygen levels.
3. Cold Stress Management – Avoid sudden temperature drops and ensure optimal brooding conditions.
4. Reduce Dust & Ammonia – Improves litter management and air quality.
5. Toxin-Free Feed – Store feed properly to prevent mold growth and mycotoxin contamination.
6. Nutritional Support – Supplement diets with Vitamin E and organic selenium to strengthen cardiovascular function.

Aspect	Breeder Birds	Broiler Birds	Layer Birds
Prevalence of Ascites	Less common due to slower growth rates.	High prevalence due to rapid growth and metabolic stress.	Low prevalence compared to broilers, but can occur in extreme cases.
Risk Factors	Genetic predisposition and environmental stress.	Fast growth, heart strain, and respiratory issues contribute to a higher risk.	Moderate risk, often related to environmental stress or poor ventilation.
Growth Rate	Slow to moderate, reducing stress on the heart and lungs.	A fast growth rate puts significant strain on the cardiovascular and respiratory systems, increasing ascites risk.	Slow to moderate growth, with a focus on egg production rather than rapid weight gain.
Heart and Lung Function	A stronger cardiovascular system suited for reproduction.	Often weak due to the rapid growth rate, contributing to ascites.	Generally stable, but stress can affect heart and lung function, leading to ascites in extreme cases.
Environmental Factors	Requires stable conditions but is less sensitive to poor ventilation compared to broilers.	Highly sensitive to poor ventilation, temperature, and humidity, increasing ascites risk.	Moderate sensitivity; poor conditions can lead to stress and health problems, including ascites.
Symptoms of Ascites	Rare, but could involve abdominal swelling if ascites occurs.	Swelling of the abdomen, labored breathing, cyanosis, lethargy, and poor weight gain.	Swelling of the abdomen is less common but may occur in stressful conditions.
Prevention	Proper environmental control, slower growth, and maintaining healthy breeding stock.	Improve ventilation, reduce rapid growth through feed management, and select for better heart health.	Maintain proper ventilation, temperature control, and stress-free environments.
Management	Focus on health monitoring, a balanced diet, and optimal breeding practices.	Address heart failure risks by controlling environmental stress and growth rates.	Manage environmental factors, ensure a balanced diet, and monitor health.
Treatment	In the case of ascites, supportive care may be required.	Treatment focuses on improving the environment and reducing stress factors; it may include medications.	In rare cases, managing environmental stress and providing care to reduce fluid buildup.

Modern Research on Ascites in Poultry

Ascites, or pulmonary hypertension syndrome (PHS), is a metabolic disorder in broiler chickens characterized by fluid accumulation in the abdominal cavity due to right ventricular failure and pulmonary hypertension. Often linked to rapid growth, high-altitude hypoxia, or environmental stressors, ascites causes significant economic losses, with global mortality rates estimated at 4.7% in broilers. Recent research from 2024–2025 explores its multifactorial causes—genetic predisposition, nutritional imbalances, and environmental triggers—while advancing diagnostics and management to reduce incidence. In the context of poultry health, ascites may occasionally contribute to splenomegaly, as both conditions reflect systemic stress and vascular congestion, making integrated control strategies critical.

Genetic and Physiological Insights

Modern studies highlight genetic predispositions driving ascites susceptibility. A 2024 University of Arkansas study used genome-wide association studies (GWAS) to identify chromosomal regions on chromosomes 2 and Z linked to ascites resistance, with candidate single-nucleotide polymorphisms (SNPs) associated with right ventricle hypertrophy. These findings enable selective breeding for resistant strains, reducing incidence without compromising growth. Physiologically, ascites stems from an imbalance between cardiac output and pulmonary vascular capacity. A 2023 transcriptomic study in Animals revealed differential gene expression in ascitic broilers’ lungs, with upregulated proinflammatory chemokines indicating an inflammatory component, potentially exacerbating splenic congestion in severe cases.

Nutritional and Dietary Advances

Nutrition plays a pivotal role in ascites prevention. A 2024 Poultry Science study demonstrated that dietary supplementation with L-arginine and vitamin C reduced tachycardia and polycythemia in broilers, lowering ascites incidence by 15% under cold stress. Similarly, a 2022 trial showed that sodium bicarbonate supplementation in drinking water ameliorated hypoxia-induced blood viscosity, easing pulmonary hypertension. High-energy diets exacerbate ascites by increasing metabolic oxygen demand, prompting research into feed restriction. A 2024 study found that early feed restriction (days 3–14) reduced ascites mortality by 20% without significantly impacting final body weight, offering a practical strategy for producers.

Environmental and Management Strategies

Environmental factors, particularly cold stress and high altitude, are major ascites triggers. A 2025 Journal of Animal Science study emphasized that maintaining optimal house ventilation and temperatures (above 15°C) during the first three weeks of life decreased ascites incidence by 25%. A 2024 Bolivian trial showed that acidifiers like Biotronic® SE reduced microbial-induced ascites by improving gut health and hygiene, cutting mortality by 10%.

Diagnostic and Preventive Innovations

Advanced diagnostics are improving ascites detection. Blood troponin T levels, indicative of myocardial damage, are now used to identify at-risk flocks, as per a 2023 study. Portable ultrasound devices enable early detection of right ventricular dilation, facilitating timely interventions. Preventive measures include genetic selection for oxygen saturation (SpO2) and low-nutrient-density diets. Research into antioxidant supplements, like coenzyme Q10 (Ascitox-Q10), showed a 2022 trial reducing winter ascites mortality by 30%, highlighting their potential in high-risk regions.

Future Directions

Ongoing research explores genomic editing to enhance pulmonary vascular capacity and anti-inflammatory feed additives to mitigate systemic stress. Integrating precision nutrition, real-time environmental monitoring, and genetic screening promises to further reduce ascites and related conditions like splenomegaly, ensuring sustainable poultry production.

Frequently Asked Questions (FAQs)

1. What is the main cause of ascites in broilers?

The primary cause is an imbalance between oxygen demand and supply due to rapid growth, poor ventilation, or cold stress.

2. Can ascites be treated?

There is no highly effective treatment, but diuretics (like frusemide) and vitamin supplementation can help manage symptoms.

3. How can farmers prevent ascites in poultry?

Preventive measures include feed restriction, ensuring proper ventilation, managing cold stress, and supplementing diets with antioxidants.

4. What are the first signs of ascites in chickens?

Early signs include stunted growth, pale head, difficulty breathing, and reluctance to move.

5. Does ascites affect egg-laying hens?

Ascites is primarily a problem in fast-growing broilers and is rarely seen in egg-laying hens.

Conclusion

Ascites in poultry remains a significant challenge in the broiler industry, mainly due to the high metabolic demands of modern broiler breeds. While no cure exists, proactive management through proper nutrition, ventilation, and environmental control can greatly reduce its incidence. By adopting these preventive strategies, poultry farmers can improve the health and welfare of their flocks while minimizing economic losses.

Reference

• Vegad, J. L. (2004).  Atlas of Poultry Diseases