Runting-stunting syndrome in broilers

Overview

Runting-Stunting Syndrome (RSS) in broilers is a multifactorial condition that affects the early growth and development of commercial poultry, particularly young broiler chickens. It is characterized by poor growth performance, uneven flock size, poor feed conversion, and visible stunted or “runted” birds. The syndrome leads to significant economic losses in the poultry industry due to reduced body weight, higher mortality, increased culling, and poor uniformity in flocks.

RSS typically appears during the first two weeks of life and can persist throughout the growing cycle. Although not considered a single disease, it is a syndrome involving various infectious agents, nutritional factors, and environmental stressors, making its control and management complex.

Causes

Runting-Stunting Syndrome is a complex condition with both infectious and non-infectious contributing factors. No single causative agent is responsible, and the syndrome is generally considered to arise from the combined impact of multiple challenges.

Infectious Causes:

• Enteric viruses: Reovirus, rotavirus, astrovirus, coronavirus, parvovirus, and adenovirus

• Bacterial infections: Clostridium perfringens, Escherichia coli

• Coccidial infections: Eimeria species may aggravate enteric damage

Non-Infectious Causes:

• Poor nutrition: Inadequate protein, vitamin, or mineral content in starter feed

• Mycotoxins: Toxins from contaminated feed (e.g., aflatoxin, ochratoxin)

• Management factors: Overcrowding, poor brooding temperatures, wet litter, and poor ventilation

• Vertical transmission: Infected breeder flocks passing viruses to progeny

Symptoms

Clinical signs of Runting-Stunting Syndrome usually become apparent within the first 7–14 days of life. Affected birds exhibit various signs that reflect poor growth, digestive dysfunction, and developmental abnormalities.

Common Signs:

• Reduced body weight and poor growth rate

• Marked size variation within the flock (uneven growth)

• Delayed feathering or abnormal feathering (e.g., “helicopter feathers”)

• Bulging or distended abdomen

• Watery droppings or mild diarrhea

• Pale or greasy appearance of the intestinal contents

Severely Affected (“Runted”) Birds May Show:

• Thin, emaciated body condition

• Stunted legs or curved spine

• Lethargy and failure to thrive

• Increased mortality or culling rates

Diagnosis

Diagnosis of Runting-Stunting Syndrome is based on flock history, clinical signs, post-mortem findings, and laboratory investigations. Because of the multifactorial nature, a comprehensive approach is required.

1. Flock and Production Data:

• Increased variability in body weights at processing

• Poor feed conversion ratios

• Early onset of growth retardation

2. Necropsy Findings:

• Distended or ballooned intestines with watery contents

• Thin intestinal walls and pale mucosa

• Pancreatic atrophy

• Liver discoloration or enlargement

3. Laboratory Testing:

• Histopathology: Villous atrophy and crypt hyperplasia in the intestines

• PCR and ELISA: To detect specific enteric viruses (e.g., reovirus, rotavirus)

• Microbiology: To identify bacterial co-infections (e.g., E. coli, Clostridium)

• Mycotoxin analysis: On feed samples to rule out toxic insults

Treatment

There is no specific treatment or vaccine for Runting-Stunting Syndrome. Management is focused on supportive care, prevention of secondary infections, and improving environmental and nutritional factors to mitigate the impact of the syndrome.

1. Supportive Management:

• Optimize brooding conditions: Temperature, humidity, and lighting

• Improve litter quality and ventilation

• Reduce stocking density to lower stress and competition

2. Nutritional Support:

• High-quality starter diets with balanced amino acids, vitamins, and minerals

• Supplement with probiotics, prebiotics, and enzymes to support gut health

• Use of acidifiers or essential oils to improve intestinal integrity

3. Control of Secondary Infections:

• Strategic use of antibiotics to control opportunistic bacterial infections

• Coccidiostats or vaccination to prevent coccidiosis

4. Biosecurity and Breeder Flock Health:

• Strict biosecurity protocols to prevent introduction of enteric pathogens

• Monitoring and improving the health of breeder flocks to prevent vertical transmission

Prognosis

The prognosis of Runting-Stunting Syndrome in broiler flocks varies depending on the severity of infection, management practices, and intervention timing. While some birds may recover partially, severely affected chicks often fail to catch up in growth and are culled. Even in recovering flocks, economic losses due to poor uniformity, reduced feed efficiency, and increased processing downgrades are common.

With improved management, nutrition, and early detection, the impact of RSS can be minimized, although complete prevention remains a challenge. Continued research is needed to better understand the underlying viral agents and develop targeted vaccines or therapies in the future.