A new wave of an enteric syndrome commonly referred to as “runting/stunting syndrome” (RSS) has emerged in the major broiler producing areas of the USA over the last four years.

Dr. John Smith, director of health and hatchery services, Fieldale Farms Corp spoke on RSS at the National Meeting on Poultry Health & Processing sponsored by the Delmarva Poultry Industry. RSS is characterized by diarrhea and severe stunting within the first one to two weeks of life, poor economic performance, and specific gross and histological lesions, and appears in many cases to be followed by secondary problems highly suggestive of immunosuppression.

Smith said that disease syndromes characterized by diarrhea and reduced growth have been recognized in commercial broilers since at least the 1970’s, and have been variously referred to as runting-stunting, pale bird, malabsorption, brittle bone, and helicopter wing syndromes. A variety of viruses have been associated with these syndromes, including reoviruses, parvoviruses, enterovirus-like viruses, rotaviruses, astroviruses, and other “small round viruses”, but a clear causal relationship has rarely been established. Many of these viruses are commonly found in healthy chickens as well.

Smith reported that RSS has been experienced by broiler complexes of several different companies in Georgia, Alabama, South Carolina, North Carolina, Arkansas and Louisiana over the last four years. RSS may have also occurred in complexes in Mississippi and Tennessee, according to Smith. Broiler operations in Great Britain, Jamaica, Mexico, and Panama also report experience with a syndrome similar to RSS.


Final feed conversion, daily gain, and uniformity are severely impacted by RSS. Direct mortality from the disease itself appears to be fairly low, but mortality from culling and from the secondary conditions can be severe.

The number of interventions attempted are literally too numerous to recall, Smith reported. The first company affected by RSS, battled with it for 3 years and has apparently recovered. This company made adjustments in breeder and pullet vaccination programs. They also obtained additional housing to increase down time, gave added attention to incubation, brooding, litter management, diet formulation, and mill sanitation and maintenance. Smith said that the manager admits that he cannot attribute the apparent success to any specific item, although down time is high on the list. Other interventions tried by other companies include attempts at prestarter antibiotic programs, litter treatments, water acidification, dietary adjustments and supplements, etc. “Of the long list, few have produced measurable results individually,” Smith said.

The reason for the eventual disappearance of RSS in some complexes is unknown, since a “shotgun” approach to treatment and prevention has generally been taken. Smith said, “One might speculate that gradual spread eventually leads to population immunity, particularly in the hens, leading to either decreased shed and/or maternal immunity, but there is currently insufficient information about either vertical shed or maternal immunity to draw any conclusions regarding the plausibility of this hypothesis.”

It has been observed that the syndrome often seems worse and persists longer in small bird complexes, Smith reported. “One might further speculate that the cycle length, irrespective of actual down time, may play a role,” Smith said.