Categories: Animal health, ArticlesPublished On: 24th June 2021

Ascites: An economic challenge

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By Given Hamnungu

Ascites is not a disease, but a multifactorial syndrome caused by the interaction of genetics, physiological and environmental conditions, and managerial factors. It is a metabolic disorder characterized by an increased workload of the cardiopulmonary system (hypoxaemia), an accumulation of fluid in the abdominal cavity, hypertrophy of the right ventricles and a flaccid heart, all of which often lead to death.

It has become a major concern to the poultry industry around the world. This condition is extremely common at high altitudes, especially during winter and cooler seasons.

Ascites develops gradually and the birds suffer for an extended period
before they die. The underlying factor to the development of these symptoms is an insufficient supply of oxygen to the tissues of a rapidly growing broiler. Environmental factors associated with poor managerial practices are the main contributors to the development of the syndrome.

Broilers that are susceptible to ascites showed reduced functionality of their tissue mitochondria. Environmental factors that increase the demand for oxygen, such as low brooding temperatures, or that impair oxygen supply to the blood, such as high altitudes, are known to increase the incidence
of ascites.

Causes of ascites

Today´s broilers grow much faster while consuming less feed. The growth rate of the heart and lungs has not increased proportionally to the growth rate of muscle and increase in body weight. The rapid growth of the bird
increases its oxygen demand, placing a bigger strain on its underdeveloped heart and lungs. Anything that limits oxygen uptake from the lungs is going
to cause the heart to work harder.

Therefore, poor ventilation in poultry sheds are the main cause of ascites because it results in:

  • The presence of ammonia in poultry sheds. Birds are unable to inhale enough oxygen, due to ammonia polluted air, resulting in inadequate blood-oxygen levels.
  • A higher concentration of dust particles in the air of poultry sheds. Birds inhale dust particles that settle in their air sacs, specifically their thoracic air sacs, causing breathing difficulties and a deficiency of oxygen.
  • High levels of carbon dioxide and low concentrations of oxygen in the air which causes insufficient oxygen absorption.

Poor ventilation can be caused by overcrowding, a lack of ventilation or
proper exhaust fans, or by blocking fresh and cold air with curtains during
winter. High altitudes have a lower concentration of oxygen and have also been known to cause heart failure and ascites.

Environmental factors

Cold temperatures
Cold exposure is the second most common cause of ascites syndrome, especially among broilers raised in open-sided and non-insulated poultry pens. When the ambient temperature is relatively lower than the bird’s body temperature, there is a sharp increase in oxygen consumption. Exposure to cold periods places birds outside of their thermo-neutral zones, increasing their demand for oxygen as they generate more energy to keep warm.

Brooding temperature
Low brooding temperatures during the 1st, 2nd and 3rd weeks increase
ascites’ mortality rate at 6 weeks of age in comparison with higher brooding temperatures.

Genetic factor
Broiler chickens have been selected for their rapid growth rate which requires more oxygen to sustain. The time required for a broiler chicken to reach 1,5 kg live weight has been reduced from 120 days in 1925 to only 30 days in 2005. Broilers’ lungs grow at a slower rate than the rest of their body, resulting in an inadequate lung capacity that cannot absorb enough oxygen for their rapid growth.

Management
Nutrient-dense rations and high feed intake is necessary for a bird to grow
faster, and cannot be ignored. Therefore, if managerial practices are not done correctly, they can cause a devastating effect on birds by causing
ascites syndrome.

Signs of ascites:

  • A high rate of panting is often observed in ascitic birds even in the absence of apparent heat stress.
  • Gurgling sounds often accompany their panting.
  • Birds which are ascitic may show sign of Cyanosis (blue discolouration of the skin), especially near the comb and wattles.
  • Ascitic birds tire out easy and often die on their bellies.
  • Most deaths occur at approximately 3 weeks of age.
  • If their belly is opened, a cup or more of fluid or jellied material will pour out.
  • The lungs of ascitic birds may often appear pale or greyish. Lungs are extremely congested and oedematous.
  • Liver enlargement is often seen.

For more information, please contact Given Hamnungu, Livestock Technical Advisor on +26(0)-975-403-834.

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