Runting-Stunting Syndrome (RSS), or malabsorption syndrome, is a critical, multi-factorial infectious poultry disease causing severe growth retardation, diarrhea, and poor feed conversion in young chickens (usually 3–21 days old). Known as “white chick syndrome” or “helicopter disease,” it results in significant economic losses, high morbidity, and flock unevenness. RSS continues to cause economic hardship in the broiler industry through decreased body weights, elevated feed conversions, reduced uniformity, reduced livability, plant downgrades and secondary diseases.

Causes

1. Viral agent

Reovirus, Rotaviruses, Avian nephritis virus, Avian astrovirus, Adenovirus, and Parvovirus

2. Bacterial agent

(Ecoli, Proteus micabilis, Enterococcus faecium, Staphylococcus cohnii, Clostridium perfringes, Bacteroides fragilis and Bacillus licheniformis) are commonly found in the intestinal tract and may cause secondary infections, aggravating the initial lesions

3. Others

Brooding at cool temperatures tends to worsen RSS symptoms, as does short down-time between flocks. Certain strains of birds appear to be more susceptible to the effects of RSS than others and male birds are more severely affected than females

Clinical signs

• symptoms of RSS can vary dramatically; birds are generally affected by RSS early in life with symptoms and mortality peaking at about 11 days.
• After placement RSS affected birds may huddle around feeders and waterers, or may persistently peck at the walls.
• Feed consumption is often depressed.
• A sizable proportion of the flock may be involved and while affected birds that are not culled may not die, they never recover.
• Often flock mortality is unaffected, but flock uniformity which normally runs about 70% decreases to about 35%.
• As feathers appear on affected birds, they are smaller than normal and may be curled especially at the wing tips (helicopter disease).
• The legs and beak of affected birds may appear pale in color (pale bird syndrome) and some birds may have rickets or broken legs (brittle bone disease)

P .M examination

• the livers are generally small, but gall bladders are enlarged.
• Intestines are thin and translucent with large amounts of fluids along with poorly digested feed present in the lumen.
• Intestines of affected birds may appear enlarged whereas the stomachs (proventriculi) may appear inflamed.
• Pancreases from diseased birds degenerate and digestive enzymes are reduced.
• Droppings from affected birds are unusually loose, vents are soiled and litter may become damp, enhancing the possibility of secondary infections.

Control of RSS

• RSS often appears suddenly and disappears equally suddenly, making it difficult to determine effective control measures. However, it is important to remember that RSS is a disease of young birds with symptoms and mortality peaking at about 11 days so control efforts should be focused early in the life of the flock. Control efforts should focus in three primary areas: Biosecurity, good poultry house management and vaccination.

• When RSS is reported in an area, it is important for the industry in the area to tighten Biosecurity procedures to reduce the possibility of exposure and to slow the spread of the disease.
• Good management starts before the birds arrive. A minimum of 12 days of downtime should be allowed between flocks. Since litter has been shown to transmit the disease, it should be removed if birds have affected with RSS.
• The brood chamber should be cleaned and disinfected as thoroughly as possible prior to chick placement. Since low brooding temperatures have been shown to worsen the effects of RSS.
• The application of vinegar or other acidifiers via water may reduce spread of the disease.
• Supplemental vitamins and minerals in both breeder and broiler feeds have also been shown to improve immunity in chicks and their ability to deal with RSS.