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Malabsorption Syndrome

Other Names: Broiler Runting Syndrome, Infectious Proventriculitis, Helicopter Syndrome, Runting-stunting Syndrome, Pale Bird Syndrome, Brittle Bone Syndrome, Femoral Head Necrosi

Malabsorption syndrome (MAS), also known as runting-stunting syndrome (RSS), is a syndrome in which a number of chickens in a flock appear considerably small and dwarf-like. MAS is most commonly seen in "meat-type" chicken breeds or broilers, and is associated with a rotavirus infection. The virus invades the intestinal mucosal cells, especially at the edges of the intestinal villi. The replication of the virus causes lysis of the bird's cells and impairing of absorption. The virus is excreted in high numbers in the feces of infected birds, and can be transmitted directly or indirectly.

Clinical Signs of Malabsorption Syndrome in Chickens

Clinical signs of MAS include growth retardation, lack of uniformity in a flock, diarrhea, low food conversion, anemia, abnormal feathering, and sometimes bone lesions. Chicks with MAS usually begin to show evidence of stunted growth at about 6-7 days of age. At this time, they may also look disoriented and pale. At about 10-12 days of age, the bodies of affected chicks are noticeably small relative to the length of the primary feathers of the wing and beak. The chick's beak and legs are much paler than the other birds. Some chicks may show "helicopter" feathers or curled wing tips, and possibly other feather abnormalities.

Common clinical signs of chickens with MAS may include:
  • Stunted growth: Where birds have much smaller bodies than other chicks.
  • Pale skin pigmentation: Chick's beak and legs appear as a paler color than normal birds.
  • Poor feathering: Chicks may have smaller than normal feathering and usually curled wing tips.
  • Leg weakness: Some affected chicks may have rickets, with weak or broken legs.
Chicks with MAS often develop secondary infections, usually with other intestinal pathogens such as Clostridium spp. or coccidia. Studies have shown that male chicks are more severely affected than females.

Clinical Signs

Stunted growth
Undigested feed in feces
Poor feed conversion ratios
Slow feathering
Broken, twisted, or curled wing tips
Eating feces
Leg weakness
Reluctance to move
Huddling around feeders and drinkers
Incessantly pecking at the walls


  • History
  • Clinical signs
  • Physical exam
  • PCR
  • Postmortem lesions


Supportive careProvide supplemental vitamins and minerals
Treatment for secondary infections.


Scientific References

Age Range

Occurs most frequently in chicks 3 to 6 weeks in age.

Risk Factors

  • Brooding at cool temperatures and short downtime between flocks - have been associated with worsening of MAS signs
  • Male chickens are more severely affected than females.