Sudden death syndrome occurs in rapidly growing young broiler chickens. The etiology is uncertain, but it may be a metabolic disorder that predisposes birds to cardiac arrhythmia. Affected birds die suddenly and have no specific gross lesions. The diagnosis is based on clinical signs and a lack of gross lesions, together with characteristic microscopic cardiac lesions. Slowing the growth rate, particularly during the first 3 weeks of life, can decrease the incidence.
A syndrome of sudden death has been reported in most areas of the world where broilers are raised intensively. It most commonly occurs in healthy, fast-growing broiler chickens, and it occurs more frequently in males. Those affected die suddenly, with a short, terminal, wing-beating convulsion. Many affected broilers just “flip over” and die on their backs. The condition is uncommon or unrecognized when low-density feed is used. Incidence can be minimized by slowing the growth rate in broilers, particularly during the first 3 weeks of life.
Etiology and Epidemiology of Sudden Death Syndrome of Broiler Chickens
The cause of sudden death syndrome of broiler chickens is poorly understood; however, it is thought to be a metabolic disease in which nutrition, genetics, and environment are contributing factors.
Sudden death syndrome of broiler chickens is linked to cardiac arrhythmias. The modern broiler, which has been selected for growth rate and feed conversion efficiency, is predisposed to developing cardiac arrhythmias. The prevalence of arrhythmias appears to be much higher in broilers than in leghorns; however, it is not clear whether this predisposition is dietary or genetic. Stress is the most likely trigger of cardiac arrhythmias in broilers, which predispose the bird to death from ventricular fibrillation.
Sudden death syndrome typically occurs in 0.5%–4% of broiler flocks.
Clinical Findings of Sudden Death Syndrome of Broiler Chickens
Broilers show no premonitory signs of sudden death syndrome. They appear healthy and may be feeding, sparring, walking, or resting when they suddenly extend their necks, gasp or squawk, and die rapidly with a short period of wing beating and leg movement, during which they frequently flip onto their backs. They also may be found dead on their sides or breasts.
Sudden death syndrome can occur as early as day 3 and may continue throughout the growing period. Cumulative flock mortality rates have been reported in the range of 0.5%–9.6%, with deaths usually peaking between the ages of 2 and 4 weeks.
Lesions
There are no specific gross lesions for sudden death syndrome. Affected birds have characteristic microscopic lesions (vacuolated sarcoplasm, cytoplasmic eosinophilia, and nuclear pyknosis) in cardiomyocytes and subendocardial Purkinje cells in the heart, and these lesions can aid in diagnosis.
Dead birds are well fleshed, have an empty or partially filled crop, and have feed in the GI tract. The abdomen is distended, and the intestines are filled with ingesta, indicating peracute death. The muscles are mottled red and white as a result of focal congestion, and the organs are moderately to severely congested. The liver may be enlarged, pale, and friable, while the kidneys are generally pale with subcapsular hemorrhage. Although the cardiac ventricles are contracted, the atria are dilated and blood-filled. The lungs are congested and frequently edematous; however, pulmonary edema increases with time after death and is not prominent in broilers examined within a few minutes postmortem. The gallbladder may be small or empty because feed intake is normal up until the time of death.
Diagnosis of Sudden Death Syndrome of Broiler Chickens
Clinical signs
Absence of gross lesions
Microscopic cardiac lesions
Sudden death syndrome should be suspected in well-grown and otherwise healthy-looking broilers found dead on their backs. That position is rare in death from other causes except cardiac tamponade, asphyxia, and ascites syndrome. Sudden death syndrome is also the likely cause when dead birds that are otherwise in good condition are found lying on their sides or breasts randomly throughout the pen.
Diagnosis is supported by necropsy findings if there is a lack of obvious pathology (ie, a digestive tract filled with ingesta, contracted ventricles, dilated and blood-filled atria, lung congestion, and edema). The presence of characteristic microscopic lesions in the heart helps to support the diagnosis. Affected cells have vacuolated sarcoplasm, cytoplasmic eosinophilia, and nuclear pyknosis.
The condition called sudden death syndrome in Australia in broiler breeders coming into production is a different disease; it is reported to be caused by potassium deficiency.
Sudden death in turkeys can be caused by aortic rupture, focal (obstructive) granulomatous pneumonia, or hypertrophic cardiomyopathy with lung congestion and edema, splenomegaly, and perirenal hemorrhage.
Prevention and Control of Sudden Death Syndrome of Broiler Chickens
Slowing the bird's growth rate
The incidence of sudden death syndrome can be minimized by slowing the growth rate of broilers, particularly during the first 3 weeks of life. Growth rate can be moderated by using the following management strategies to control nutrient intake:
decreasing the number of hours of light per day
decreasing the energy and protein levels in the diet
restricting the amount of feed provided
Key Points
The cause of sudden death syndrome is uncertain, but it is likely a metabolic disease.
Incidence can be decreased by slowing the growth rate.
No pathognomonic lesions or diagnostic tests are available.
For More Information
Crespo R. Developmental, metabolic, and other noninfectious disorders. In Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:1303-1304.
Shivaprasad HL. Cardiovascular diseases: sudden death syndrome in broiler chickens. In: Brugere-Picoux J, Vaillancourt JP, Shivaprasad HL, Venne D, Bouzouaia M, eds. Manual of Poultry Diseases. French Association for the Advancement of Science (AFAS); 2015:463-464.
Sosnowka-Czajka E, Skomorucha I. Sudden death syndrome in broiler chickens: a review on the etiology and prevention of the syndrome. Annals Anim Sci. 2022;22:865-871.
Olkowski AA. Pathophysiology of heart failure in broiler chickens: structural, biochemical, and molecular characteristics. Poult Sci. 2007;86(5):999-1005.
