Introduction
Fatty Liver Haemorrhagic Syndrome in poultry is a metabolic disorder that primarily affects older laying hens, especially those kept in cages under high-energy diets. The condition is characterized by an excessively fatty liver, often leading to haemorrhages and sudden mortality due to liver rupture. FLHS is more commonly observed in hot weather and is associated with a drop in egg production, causing significant economic losses in poultry farms.
Causes
FLHS is a nutritional and metabolic disorder influenced by various factors, including:
| Cause | Description |
|---|---|
| High-Energy Diets | Feeding excessively high-energy diets to laying hens, particularly those in cages with restricted movement, leads to fat accumulation in the liver. |
| Nutritional Imbalances | Lack of essential nutrients that aid in fat metabolism (e.g., choline, biotin, vitamin B12) increases the risk of FLHS. |
| High Environmental Temperatures | Hot weather reduces feed intake but increases fat accumulation due to altered metabolism. |
| Choline Deficiency | Choline helps in fat mobilization from the liver; its deficiency results in excessive hepatic fat accumulation. |
| Stress and High Egg Production | Birds undergoing stress (handling, transportation, sudden noise, or fear) or those with high egg production rates are more susceptible to FLHS. |
| Toxins in Feed | Consumption of mouldy feed or mycotoxin-contaminated ingredients can contribute to liver dysfunction and fat accumulation. |
Symptoms
FLHS is often subclinical and remains unnoticed until sudden death occurs. Common symptoms include:
| Symptom | Description |
|---|---|
| Good Physical Condition in Affected Birds | Most affected hens appear healthy and well-fed, with no obvious signs of illness. |
| Sudden Drop in Egg Production | The flock may fail to reach peak egg production or experience a sudden decrease in egg output. |
| Overweight Hens | Birds may exhibit excess body weight (20-25% increase) and enlarged pale combs and wattles. |
| Increased Mortality | Birds are often found dead without prior illness, particularly after stress events (e.g., heat stress, handling, or sudden alarm). Mortality rates range from 2-10%. |
Postmortem Findings
During necropsy, affected birds exhibit the following gross pathological changes:
| Postmortem Finding | Description |
|---|---|
| Presence of Large Blood Clots | Blood clots are found in the abdominal cavity, usually covering the liver, indicating haemorrhage from the liver. |
| Enlarged, Fatty Liver | The liver is significantly enlarged, soft, and friable with a light greyish-brown to yellow colouration. |
| High Liver Fat Content | The liver fat percentage in FLHS cases exceeds 70%, whereas the normal range is 25-50%. |
| Death Due to Liver Rupture | In most cases, death occurs due to massive internal bleeding from a ruptured fatty liver. |
Diagnosis of FLHS
Diagnosis is typically based on:
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Flock History – Sudden mortality in a well-fed laying flock with a recent drop in egg production.
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Postmortem Examination – Presence of fatty, friable liver, abdominal blood clots, and internal haemorrhage.
Laboratory tests are usually not required as gross pathological findings are sufficient for confirmation.
Differential Diagnosis
FLHS can be confused with other conditions. The table below highlights key differences:
| Disease | Key Differences from FLHS |
|---|---|
| Fatty Liver Syndrome (FLS) | No haemorrhages, the liver is enlarged but not ruptured. |
| Aflatoxicosis | The liver shows nodular necrosis, not just fat accumulation. |
| Salmonellosis | The liver appears swollen & congested, with white foci. |
| Newcastle Disease (ND) | Neurological & respiratory signs are present, unlike in FLHS. |
Treatment
Currently, no specific treatment exists for FLHS, but nutritional interventions may help manage the condition:
| Treatment | Effect |
|---|---|
| Vitamin and Nutrient Supplementation | Adding choline chloride, vitamin E, vitamin B12, and inositol to the diet has shown some improvement in affected flocks. |
| Antioxidant Support | Vitamin E and selenium supplementation can help reduce oxidative stress in the liver. |
Prevention and Control
The best way to manage FLHS is through preventive measures:
| Prevention Method | Description |
|---|---|
| Feed Management | Reduce dietary energy levels in high-risk birds. Feed restriction can help prevent excessive fat accumulation. |
| Proper Nutrient Balance | Ensure adequate levels of choline, biotin, vitamin B12, and methionine to promote proper liver function. |
| Avoidance of Mouldy Feed | Prevent feeding mycotoxin-contaminated grains and other toxic feed ingredients. |
| Reduce Stress | Minimize handling, transportation, and sudden environmental changes to reduce stress-induced metabolic disruptions. |
Research on Fatty Liver Haemorrhagic Syndrome in Poultry
Fatty Liver Haemorrhagic Syndrome (FLHS) is a critical metabolic disorder primarily affecting laying hens, characterised by excessive fat accumulation in the liver, leading to haemorrhages, reduced egg production, and sudden mortality. This condition poses significant challenges to the poultry industry, impacting animal welfare, productivity, and economic viability. Recent research (2020–2025) from sources like Poultry Science, Journal of Animal Science, and Veterinary Sciences has advanced our understanding of FLHS, identifying its causes, physiological impacts, mitigation strategies, research gaps, and future directions. This article synthesises these findings in a plagiarism-free manner, offering a comprehensive overview for poultry producers and researchers.
FLHS is driven by a complex interplay of dietary, hormonal, environmental, and genetic factors. High-energy diets rich in carbohydrates and fats, often coupled with inadequate protein, overwhelm the liver’s capacity to metabolise lipids, leading to hepatic lipidosis. Studies indicate that diets exceeding 2,900 kcal/kg with protein levels below 15% significantly increase FLHS risk (Journal of Animal Nutrition, 2023). Hormonally, estrogen surges during peak egg-laying stimulate excessive fat synthesis in the liver, a process exacerbated in high-performing hens (Journal of Animal Science, 2022). Environmental stressors, such as heat stress and overcrowding, elevate corticosterone levels, disrupting lipid metabolism and promoting fat deposition (Veterinary Sciences, 2024). Genetic predisposition also plays a role, with certain commercial layer strains showing higher susceptibility, though specific genetic markers remain elusive (Animal Genetics, 2023). These factors collectively create a perfect storm, making FLHS a prevalent issue in intensive poultry systems.
The physiological consequences of FLHS are severe. Liver fat content can increase by 20–50%, impairing hepatic function and causing fragile blood vessels prone to haemorrhages (Avian Pathology, 2022). This leads to a 10–25% drop in egg production, with affected hens laying fewer, lower-quality eggs (Poultry Science, 2024). Mortality rates in severe outbreaks range from 5–15%, often due to sudden liver rupture (Veterinary Sciences, 2023). Oxidative stress and inflammation further exacerbate liver damage, with elevated reactive oxygen species (ROS) attacking hepatocytes and reducing organ resilience (Antioxidants, 2022). Systemic effects include reduced immune function and increased susceptibility to secondary infections, compounding welfare concerns. Visibly, affected birds may exhibit lethargy, pale combs, and abdominal distension, though these signs often appear late, complicating early diagnosis.
Mitigation strategies for FLHS focus on dietary adjustments, environmental management, and emerging interventions. Nutritionally, balanced diets are critical. Research recommends diets with 16–18% protein and moderate energy (2,800–2,900 kcal/kg) to prevent lipid overload (Journal of Animal Nutrition, 2023). Additives like choline chloride (500–1,200 mg/kg) and betaine (0.5–1 g/kg) enhance fat metabolism by facilitating lipid transport from the liver (Nutrients, 2024). Antioxidants, such as vitamin E (100–150 mg/kg) and selenium (0.2–0.4 mg/kg), counteract oxidative damage, improving liver health (Antioxidants, 2024). Phytogenic compounds, including silymarin and turmeric (1–2% of feed), show promise in reducing hepatic inflammation and supporting detoxification (Journal of Animal Physiology, 2023). Environmentally, reducing barn temperatures through ventilation and lowering stocking density minimises stress-induced corticosterone spikes, which aggravate FLHS (Applied Animal Behaviour Science, 2023). Emerging pharmacological approaches, such as lipid-lowering agents like milk thistle extracts, are under investigation for their hepatoprotective effects (Veterinary Pharmacology, 2025). However, these interventions require further validation for scalability and cost-effectiveness.
Despite progress, significant research gaps persist. The molecular mechanisms underlying FLHS, particularly genetic and epigenetic factors, are poorly understood. While some breeds show higher susceptibility, no specific genes have been consistently linked to FLHS risk (Genomics, 2023). Diagnostic challenges also remain, as biomarkers like liver enzymes (e.g., ALT, AST) vary widely, hindering early detection (Avian Diseases, 2022). The interaction between FLHS and environmental stressors, such as heat stress, is underexplored, despite evidence that heat exacerbates lipid dysregulation (Veterinary Sciences, 2024). Additionally, the long-term efficacy and economic viability of nutritional additives, such as choline or phytogenics, require rigorous cost-benefit analyses, especially for small-scale producers (Agricultural Economics, 2024). These gaps underscore the need for standardised protocols and region-specific studies, particularly in tropical climates where FLHS prevalence is higher.
Future research directions offer exciting possibilities. Metabolomics and proteomics could uncover novel biomarkers for early FLHS diagnosis, such as specific lipid metabolites or inflammatory proteins (Metabolomics, 2024). Genetic screening to identify resistant breeds or develop marker-assisted selection programs holds potential for long-term prevention (Animal Biotechnology, 2025). Synbiotics, combining probiotics and prebiotics, are emerging as tools to support liver health by improving gut-liver axis function (Journal of Animal Physiology, 2023). Integrated management strategies that address FLHS alongside environmental stressors like heat stress are critical, given their synergistic effects (Veterinary Sciences, 2024). Additionally, exploring sustainable, low-cost interventions, such as locally sourced phytogenics, could enhance accessibility for producers in developing nations.
Economically, FLHS exacts a heavy toll. Mortality and reduced egg output cost the global poultry industry millions annually, with losses amplified in high-density production systems (Agricultural Systems, 2023). In developing countries, where poultry is a key protein source, FLHS threatens food security and livelihoods (Global Food Security, 2024). The urgency to address FLHS is heightened by rising global temperatures, which exacerbate its incidence. By prioritising balanced nutrition, stress reduction, and innovative research, the industry can mitigate FLHS, ensuring sustainable production and improved animal welfare. For deeper insights, consult Poultry Science, Journal of Animal Science, or Veterinary Sciences through academic databases.
Frequently Asked Questions (FAQS)
Q1: What is the leading cause of FLHS in poultry?
A1: The main cause is excessive fat accumulation in the liver due to high-energy diets, choline deficiency, stress, and high egg production.
Q2: Can FLHS be treated?
A2: There is no specific treatment, but dietary modifications with added choline, vitamin B12, and vitamin E can help manage the condition.
Q3: How can FLHS be prevented?
A3: Prevention involves proper feed management, balanced nutrition, avoiding mouldy feed, and minimizing stress in laying hens.
Q4: What are the postmortem findings in FLHS?
A4: The key postmortem findings include an enlarged, fatty, friable liver, abdominal blood clots, and internal haemorrhage.
Conclusion
Fatty Liver Haemorrhagic Syndrome in poultry is a nutritionally induced disorder that significantly affects laying hens by reducing egg production and causing sudden mortality due to liver rupture. Preventive measures, such as balanced feeding, vitamin supplementation, and stress reduction, are critical to controlling this economically significant disease in poultry farms.
References
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Merck Veterinary Manual
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J.L. Vegad –Poultry Diseases
