Diagnosing SDS in Broiler Chickens
Chickens exhibit no prior signs before death. They appear perfectly healthy; they might be feeding, fighting, walking, or resting when suddenly they extend their necks, gasp, or chirp. Immediately after, they lose their balance, convulse, and flap their wings wildly. In most cases, the birds fall onto their backs (flip-over) and die with one or both legs raised.
If healthy, growing broiler chickens are suddenly found dead on their backs, Sudden Death Syndrome should be considered. This condition is rarely seen in deaths due to other causes, except for cardiac tamponade, suffocation, and ascites syndrome.
Article: For more information, you can read the article on poultry ascites
Clinical Findings of Sudden Death Syndrome (SDS) in Broiler Chickens: Diagnostic Methods
Accurate diagnosis of SDS is achieved post-mortem through tissue examination. Birds that die from SDS have well-fleshed carcasses. Their gizzards are empty or partially filled, and feed is present in the digestive tract. The abdomen is distended, and the intestines are full of food, indicating an acute and sudden death. Due to blood vessel engorgement (congestion), the bird’s muscles appear mottled red and white and are severely swollen.
The liver may be enlarged, pale, and friable, while the kidneys are typically pale with subcapsular hemorrhages. Although the heart ventricles are contracted, the atria are dilated and engorged with blood. The lungs are congested and often edematous; however, pulmonary edema increases post-mortem and is not prominent in broilers examined minutes after death. In pulmonary edema, fluid accumulates in the lung sacs, causing breathing difficulties. The gallbladder may be small or empty, as feed consumption is normal until death.
If no obvious gross lesions are present (such as a digestive tract full of feed, contracted ventricles, dilated and blood-engorged atria, lung congestion, and edema), diagnosis is established through necropsy findings. The presence of distinct microscopic lesions in the heart aids in diagnosis. Damaged cells exhibit vacuolated sarcoplasm, cytoplasmic eosinophilia, and nuclear pyknosis.
In turkeys, sudden death can result from aortic rupture, localized granulomatous pneumonia (obstruction), or hypertrophic cardiomyopathy with pulmonary congestion and edema, splenic enlargement, and perirenal hemorrhage.
What are the Main Causes of Sudden Death Syndrome (SDS) in Broiler Chickens?
Sudden Death Syndrome in broiler chickens has been recognized as a pathophysiological entity for four decades. The exact cause of SDS in broiler chickens is not fully understood. SDS typically occurs in 0.5% to 4% of broiler flocks.
Recent research links SDS to cardiac arrhythmias. A 2008 study on the pathogenesis of SDS in susceptible broiler chickens assessed the susceptibility of broiler chickens to cardiac arrhythmias under stress conditions using an epinephrine-simulated stress test.
This challenge revealed that many broiler chickens are susceptible to stress-induced cardiac arrhythmias. In some chickens, the stress challenge caused severe ventricular arrhythmias. Chickens that exhibited the most severe arrhythmic response died suddenly within a few days.
Overall, research indicates that stress is the most likely trigger for cardiac arrhythmias in broiler chickens. In this regard, the rapid growth rate of modern broiler chickens creates highly favorable conditions for sustained ventricular arrhythmias. Consequently, the combination of stress, cardiac arrhythmia changes, and alterations in the His-Purkinje system, located in the ventricular walls of the heart, are significant factors in SDS. Ultimately, fast-growing broiler chickens exhibit a high incidence of cardiac dysrhythmias.
In essence, this disease is associated with cardiac arrhythmias (irregular heart rhythm).
Today, according to research, scientists have identified the following factors as contributing to sudden chicken death:
- Metabolic Disorders: The syndrome stems from a metabolic disorder that prevents the chicken’s body from properly processing nutrients. This disorder can lead to the accumulation of waste products in the body, ultimately resulting in death.
- Heart Problems: Cardiac issues such as arrhythmias (irregular heartbeats) may play a role in the development of this syndrome. The rapid growth of broiler chickens and the strain on their cardiovascular system may contribute to these problems.
- Nutrition: Inadequate nutrition and deficiencies in certain nutrients can also increase the risk of developing this syndrome.
Factors Increasing the Risk of Sudden Death Syndrome (SDS) in Poultry
Sudden Death Syndrome (SDS) typically arises from a combination of several factors. However, it remains unclear whether this susceptibility is due to dietary or genetic factors. According to research to date, the following are identified as exacerbating factors for Sudden Death Syndrome in chickens:
- High Growth Rate: A significant factor in broiler chicken SDS is rapid growth. This rapid growth can place excessive strain on bodily systems, particularly the cardiovascular system.
- Overfeeding: Excessive and high-energy feeding can lead to metabolic disorders and increase the risk of SDS. Using less dense feed has been shown to significantly reduce the likelihood of outbreaks. Therefore, slowing the growth rate of broiler chickens during the first three weeks of rearing is crucial.
- Stressors: Stress, as a primary trigger for cardiac arrhythmias in broiler chickens, can predispose birds to death from ventricular fibrillation. Any stressor, such as high-density flocks, lack of mobility, sudden or excessive noise, etc.
- Poultry Sex: Research has shown that this disease is more prevalent in male chickens. Approximately 70% of affected birds are male.
- Chicken Breed: In general, the prevalence of cardiac arrhythmias is significantly higher in broiler breeds than in laying breeds. Furthermore, in a study published in the journal Poultry Science by ScienceDirect, an experiment was conducted on the susceptibility to metabolic disorders in various strains of male broiler chickens. In this experiment, all chickens were male and from the Arbor Acres (A-Plus), Cobb-500, Hubbard-Peterson, ISA, Naked Neck, and Ross breeds.
The experiment revealed that the total mortality rate among high-producing broiler chickens was high, with over 50% due to Sudden Death Syndrome (SDS) and Ascites Syndrome. No Naked Neck birds were lost due to these disorders, and overall mortality was significantly lower than in other strains. The most notable difference observed among the tested strains was the lower weight and higher feed conversion of Naked Neck broiler chickens. - Diet: A high-energy diet, especially in the early weeks when growth rate is accelerated, as well as diets high in glucose versus starch, are contributing factors. Additionally, research has shown that the incidence of this disease is higher in flocks with wheat-based diets than in those using corn in their feed.
What Treatment Measures Exist for Sudden Death Syndrome (SDS) in Poultry?
Given that this syndrome involves sudden death, no treatment or solution has been found to date. According to research, prevention is considered the best approach.
Prevention and Control of Poultry Stroke: What Measures Can Be Taken to Reduce Losses from This Syndrome?
An article titled “Sudden Death Syndrome in Broiler Chickens: A Review of Cause and Prevention” published in 2022, states that the only preventive measure to date is to reduce profitability by limiting feeding and extending the growth period.
The incidence of SDS can be minimized by monitoring and controlling the growth rate of broiler chickens, especially in the first 3 weeks of life. Be sure to compare the bird’s weight gain and growth with the catalog. If the chicken’s weight gain is unreasonably higher than the growth catalog, consider the following management strategies to control and prevent SDS:
- Increased periods of darkness to reduce feed consumption.
- Reduced carbohydrate and protein energy levels in the diet.
- Managed and restricted feeding.
- Reduction of stressors in chickens (such as sudden noises, heat stress, etc.).
- Low-intensity lighting, the use of dawn-to-dusk simulation, and avoidance of disturbances for laying hens.
Sudden Death Syndrome is a serious problem in the broiler chicken farming industry. Its exact cause is not yet known and requires further research. Future research should focus on developing effective prevention methods and reducing the susceptibility of broiler chickens to this syndrome. Finally, consider that in higher altitude areas, controlling the diet and reducing food energy is very important. The likelihood of birds developing SDS and ascites is higher in these areas. Reducing feed consumption and slowing the growth process, especially in the early weeks, are critical issues at this time.
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