Chicken Diarrhea Causes

Diarrhoea (or diarrhea) is one of the most frequent clinical signs observed in backyard chickens and can indicate anything from a minor dietary indiscretion to a life-threatening infectious disease. As a veterinary professional, it is critical to help poultry owners distinguish between self-limiting episodes and conditions that demand immediate intervention. This pillar article provides a comprehensive, evidence-based overview of the causes of chicken diarrhoea, with particular emphasis on diet, parasites (especially coccidia), heat stress, and red flags that signal the need for urgent veterinary care. Recommendations are drawn from authoritative guidelines including those of the American Veterinary Medical Association (AVMA) [1], the Merck Veterinary Manual [2], and the European Food Safety Authority (EFSA) [3]. Both North American and Commonwealth terminology (e.g., diarrhea vs. diarrhoea) are used throughout to serve a global audience.

Quick Q&A

Question: What are the most common causes of diarrhea in chickens?
Answer: The most frequent causes include dietary changes (e.g., sudden introduction of treats or high-protein feeds), coccidiosis (a protozoal infection), heat stress, and bacterial infections such as salmonellosis. Identifying the underlying cause requires evaluation of the bird's history, environment, and faecal characteristics, often with laboratory diagnostics.

Dietary Causes of Diarrhea in Chickens

Nutritional mismanagement is one of the most common and easily correctable reasons for loose droppings in backyard flocks. Chickens have a relatively simple digestive tract, and their intestinal microbiota is sensitive to abrupt alterations.

Sudden Diet Changes

Abruptly switching from a standard layer ration to a high-protein grower feed, or introducing large quantities of fresh greens, fruits, or kitchen scraps, can overwhelm the gut's ability to absorb water and electrolytes. The result is a transient, watery diarrhoea that typically resolves within 24 to 48 hours if the original diet is restored. According to the Merck Veterinary Manual [2], a gradual transition over 7 to 10 days is recommended when changing feed types.

High-Protein Feeds and Treats

Feeding excessive protein (above 18% in adult layers) or offering too many treats such as mealworms, corn, or bread can cause osmotic diarrhoea. This occurs because undigested protein and carbohydrates draw water into the intestinal lumen. In Australia and Europe, where many backyard flocks are kept on pasture, over-reliance on supplemental grains is a common trigger.

Toxic Plants and Moldy Feed

Ingestion of mouldy grain contaminated with mycotoxins (e.g., aflatoxins, vomitoxin) can lead to severe diarrhoea and systemic illness. Similarly, certain plants like avocado pits, rhubarb leaves, and raw potatoes contain toxins that irritate the gastrointestinal tract [4]. The AVMA advises keeping feed stored in cool, dry conditions and discarding any feed with visible mould or off-odours.

Parasitic Infections

Parasites are a leading cause of chronic or recurrent diarrhoea in backyard poultry worldwide. Coccidiosis, in particular, is the most significant parasitic disease affecting chickens.

Coccidiosis

Caused by protozoa of the genus Eimeria, coccidiosis is a major concern for both commercial and backyard flocks. The parasite invades the intestinal epithelium, causing sloughing of cells, haemorrhage, and malabsorption. Clinical signs include watery or bloody diarrhoea (often described as "chocolate-coloured"), ruffled feathers, huddling, and reduced egg production. In severe cases, mortality can be high, especially in young birds aged 3 to 6 weeks [5].

Diagnosis is confirmed by faecal flotation revealing oocysts, though intermittent shedding can yield false negatives. The CFIA (Canadian Food Inspection Agency) and EFSA emphasise that biosecurity measures, such as keeping feeders and waterers clean and rotating pasture, are crucial for control [3]. Anticoccidial drugs (e.g., amprolium) are available for treatment but must be used judiciously to avoid resistance.

Roundworms and Other Helminths

Large roundworms (Ascaridia galli) and caecal worms (Heterakis gallinarum) can cause diarrhoea when burdens are heavy. Heterakis also serves as a vector for Histomonas meleagridis, the agent of blackhead disease (histomoniasis). Although turkeys are more susceptible, chickens can also develop histomoniasis, which presents with yellow, sulphur-coloured diarrhoea and listlessness. Deworming with fenbendazole or levamisole, combined with good sanitation, is advised by the AAHA guidelines for avian practice.

Bacterial and Viral Infections

Infectious agents can cause profuse, foul-smelling diarrhoea that often requires veterinary attention and case-specific treatment.

Salmonellosis

Salmonella species (including S. enteritidis and S. typhimurium) are zoonotic pathogens that cause diarrhoea in chickens. Infected birds may show loose, greenish droppings, lethargy, and decreased appetite. In many jurisdictions, including the United States and the European Union, salmonellosis is a reportable disease. The AVMA recommends faecal culture and serotyping for definitive diagnosis [1]. Treatment is controversial because of public health concerns; some regulatory agencies advise euthanasia of positive flocks, while others permit antibiotic therapy under veterinary supervision.

Colibacillosis

Escherichia coli infections are often secondary to other stressors (e.g., coccidiosis, poor ventilation). Affected birds exhibit watery diarrhoea, omphalitis (yolk sac infection) in chicks, and septicaemia. Supportive care and appropriate antibiotics based on culture and sensitivity are essential.

Viral Diseases

• Newcastle disease: Virulent strains cause respiratory signs accompanied by greenish, watery diarrhoea. It is a notifiable disease internationally.
• Avian influenza: Highly pathogenic strains produce severe diarrhoea, oedema, and high mortality. The DAFF (Australian Department of Agriculture, Fisheries and Forestry) and the CVMA (Canadian Veterinary Medical Association) stress immediate reporting of suspicious cases.

Heat Stress and Environmental Factors

Heat stress is a common but often overlooked cause of diarrhoea in chickens during summer months. When ambient temperatures exceed 30°C (86°F) and humidity is high, chickens pant to dissipate heat, leading to respiratory alkalosis and compensatory renal excretion of bicarbonate. This alters gut ion transport, resulting in increased water content in droppings.

Additional environmental triggers include:

• Poor ventilation: Accumulation of ammonia from litter can irritate the respiratory tract and indirectly affect gut health.
• Water deprivation: Dehydration followed by sudden access to water can cause osmotic diarrhoea.
• Stress from handling or predator attacks: Stress hormones alter gut motility and permeability.

According to the Cornell College of Veterinary Medicine, providing shade, increasing air circulation, and offering cold water during heat waves can significantly reduce the incidence of diarrhoea caused by heat stress.

Red Flags: When to Seek Veterinary Care

Not every loose dropping requires a trip to the veterinarian, but certain signs indicate a serious underlying condition. Poultry owners should be educated to recognise these red flags:

Bloody or Black Tarry Stools

Blood (fresh red or digested black) suggests coccidiosis, heavy worm burdens, or bacterial enteritis. Immediate veterinary evaluation is warranted.

Severe Dehydration

Signs include sunken eyes, dry comb/wattles, and skin that remains elevated after pinching. Dehydration can rapidly become fatal.

Sudden Drop in Egg Production or Shell Quality

When diarrhoea is accompanied by a sharp decrease in laying or thin-shelled eggs, infectious agents like Salmonella or Mycoplasma should be suspected.

Lethargy and Flock-Wide Illness

If multiple birds show diarrhoea along with depression, head tremors, or respiratory signs, a notifiable disease must be ruled out. In the UK and EU, the FVE (Federation of Veterinarians of Europe) advises immediate contact with the local animal health authority.

Prolonged Diarrhoea (More Than 48 Hours)

Chronic diarrhoea lasting more than two days without improvement, despite dietary modification, requires diagnostic investigation including faecal flotation, culture, and possibly necropsy.

Diagnostic Approach

A systematic diagnostic workup should include:

• History and physical exam: Evaluate diet, recent changes, environment, vaccination status, and clinical signs.
• Faecal examination: Direct smear and flotation for oocysts (coccidia), nematode eggs, and protozoal trophozoites.
• Bacterial culture: For Salmonella, E. coli, and Campylobacter – especially important if zoonotic risk is a concern.
• Necropsy: In flock outbreaks or when a single bird dies, necropsy provides invaluable information on intestinal lesions, presence of haemorrhage, and evidence of systemic disease.

The American Association of Avian Pathologists (AAAP) publishes diagnostic guidelines that are followed by most veterinary diagnostic laboratories.

Treatment and Management

Treatment depends entirely on the underlying cause. Non-specific supportive care is always indicated:

• Fluid therapy: Offer electrolyte solutions (commercial or homemade: 1 L water, 1 tsp salt, 1/2 tsp baking soda, 1 tbsp sugar). In severe cases, subcutaneous or intracoelomic fluids can be administered by a vet.
• Probiotics: Lactobacillus-based products can help restore normal gut flora after antibiotic therapy or diet change.
• Dietary modification: Temporarily withhold treats and feed a simple, high-quality complete feed. Adding plain yoghurt (if birds are not lactose intolerant) may aid digestion.

Specific treatments include:

• Coccidiosis: Amprolium (Corid) in water for 5 to 7 days. Avoid using it as a prophylactic in healthy birds unless on the advice of a veterinarian.
• Worms: Fenbendazole (Safe-Guard) or ivermectin (though ivermectin is less effective against tapeworms – use praziquantel instead).
• Bacterial infections: Antibiotic therapy should be based on culture and sensitivity. Use of antibiotics in food-producing animals must comply with local withdrawal periods (e.g., FDA regulations in the US, CFIA in Canada, EMA in Europe).
• Heat stress: Provide shade, fans, cold water, and electrolyte supplements. Avoid handling birds during the hottest part of the day.

Prevention

Preventive strategies are far more effective than treating disease outbreaks. Key recommendations from the AVMA, AAHA, and European poultry health consortia include:

• Biosecurity: Limit visitors, quarantine new birds for at least 30 days, and disinfect footwear and equipment.
• Clean water and feed: Use nipple drinkers or regularly cleaned open waterers. Store feed in rodent-proof containers.
• Vaccination: Coccidiosis vaccines (administered by spray or in feed) are available for replacement pullets. Consult a poultry veterinarian about local prevalence and vaccine options.
• Pasture rotation: Move birds to fresh ground to break parasite life cycles. Avoid wet, muddy areas that favour coccidia sporulation.
• Regular health monitoring: Inspect droppings daily. A sudden change in colour, consistency, or odour warrants investigation.

In conclusion, diarrhoea in chickens is a multifactorial clinical sign ranging from benign dietary indiscretions to severe parasitic, bacterial, or viral infections. A methodical approach considering the bird's age, diet, environment, and faecal characteristics is essential. By recognizing red flags early and implementing evidence-based prevention and treatment protocols, veterinary professionals and dedicated poultry owners can safeguard flock health and minimise losses.

References

[1] American Veterinary Medical Association (AVMA). Poultry Health and Biosecurity Guidelines. 2022.
[2] Merck Veterinary Manual. Digestive Disorders of Poultry. 11th ed. Kenilworth, NJ: Merck & Co., Inc.; 2023.
[3] European Food Safety Authority (EFSA). Scientific Opinion on the Welfare of Laying Hens. EFSA Journal 2023;21(4):e07982.
[4] Cornell University College of Veterinary Medicine. Backyard Poultry Health: Common Toxins. Ithaca, NY; 2021.
[5] Canadian Food Inspection Agency (CFIA). Coccidiosis in Poultry: Diagnosis and Control. Ottawa, ON; 2022.
[6] DVM360 / VCA Animal Hospitals. Managing Diarrhea in Chickens. 2020.
[7] Federation of Veterinarians of Europe (FVE). Avian Health Guidelines for Practitioners. Brussels, Belgium; 2021.
[8] American Association of Avian Pathologists (AAAP). Diagnostic Manual of Avian Diseases. 6th ed. Jacksonville, FL; 2020.