Ascites in commercial broiler poultry and its management

Dr.Kedar Karki

Metabolic diseases affect internal body metabolism and development, and are the cause of a large portion of mortality in commercial poultry flocks. Two of the more important types of metabolic diseases are the cardiopulmonary disorders: sudden death sundrome and ascites. Certain types of leg problems are also related to metabolic distrubances.

Ascites is most commonly seen in fast growing broilers and is characterised by the accumulation of fluid in the abdominal cavity. Although the disease is not fully understood, this heart failure is thought to be a consequence of a lowered oxygen tension in poultry houses and birds suffering from too little oxygen. Poor ventilation is a major contributory factor. When the disease was first observed, it was seen mainly in areas of higher altitude and in fast growing broilers although it now occurs at all altitudes. Cold temperatures, coupled with high energy diets, can result in ascites-related deaths as a consequence of insufficient pulmonary vascular capillary capacity for the blood flow necessary to meet a high metabolic oxygen requirement.

In the World Broiler Ascites Survey information on 18 countries from four continents showed that ascites affects 4.7% of live broilers worldwide. The cost to the worldwide broiler chicken industry due to ascites related mortality has been estimated to be in excess of $500 billion per year.

Ascites is not a disease, it is a condition in which excess amount of ascitic fluids (a combination of lymph and blood plasma which has leaked from the liver) accumulate in the body cavity. In broiler chickens, the condition often leads to death. The ascites syndrome is associated with abnormally high blood pressure between the heart and lungs (pulmonary hypertension) leading to right heart failure, increased blood pressure in the veins, and excessive buildup of fluid in the liver (passive liver congestion) which leaks into the body cavity.

The incidence of ascites has increased worldwide over the past several years. This increase coincides with ongoing genetic and nutritional improvements in the areas of growth rate and feed efficiency.

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Meat-type chickens are selected for growth rate and muscle mass. Due to very successful genetic selection techniques, growth rate has increased at a rate of 4 to 5% per year over the past 30 years. Broiler performance (average of both sexes) has improved so much that the growing period to produce broilers of the same weight has decreased by 30% in just 15 years. A 2kg. bird took 56 days to produce in 1976; it can now be produced in less that 42 days. Selection for rapid growth and efficient feed conversion has resulted in a broiler with such a high rate of metabolism that its heart and lungs are barely capable of providing enough oxygen to sustain the body.

Contributing Factors:

 

The genetics of meat birds has changed dramatically in the last ten years. Today's broilers grow much faster, eating less feed. The growth of the heart and lungs has not increased in size proportional to the increase in body weight and breast meat yield. The rapid growth of the bird means more oxygen demand, requiring more work out of the heart and lungs.

High basal metabolic rate High sodium/salt content in water/feed-Excess levels of sodium

in the water or slat in feed leads to increased blood pressure in the lungs. Levels of sodium over 400 ppm could cause problems in broilers.

High altitudes have long been known to cause heart failure and ascites.

Chilling is a common cause in small flocks. It causes an increased blood flow through the lungs.

High energy rations Vitamin E deficiency Environmental factors

1. Temperature : Careful attention to brooding temperatures is critical in the prevention of ascites. Low temperature brooding forces the birds to use energy (which requires oxygen) in order to maintain body temperatures. This predisposes a flock of broilers to ascites, although the signs of ascites show up later in production. Air temperature is also important later in production, but it is especially critical early.

2. Air Quality : Any further challenges to the bird's ability to exchange oxygen with its environment predispose it to ascites.

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o Dust - Dusty environments can contribute to the onset of ascites. Disease causing microorganisms can also attach themselves to dust particles, and be respired, causing irritation or infection in the lungs. This further reduces oxygen transfer between the bird and the environment.

o Ammonia - High levels of ammonia in the broiler house can irritate the lungs, resulting in decreased oxygen transfer between the bird and the environment.

o Oxygen - Natural gas open-flame brooders contribute to oxygen depletion in broiler houses. This burning of oxygen is in direct competition with the birds. Ventilation rates must supply enough air to replenish the oxygen consumed. The volume of air coming in the air intakes should be uniformly distributed to the birds. Proper levels of oxygen typically coincide with low levels of ammonia and respirable dust. Adequate air exchange must be provided to broilers as a preventive method of ascites. Because broilers have rapid growth rates, adequate oxygen levels are essential to prevent increased stress on the respiratory system and consequently the heart.

o Carbondioxide

 

Diagnosis:

Ascites is most commonly diagnosed at 4 - 5 weeks of age, although signs of ascites have been recorded in day-old birds Low oxygen status of embryos during incubation may be related to the onset of ascites. Panting is often observed in ascitic birds even in the absence of apparent heat stress. This panting in ascitic birds is due to physical restriction of the large abdominal air sacs. The excessive abdominal fluid accumulation results in a reduction in the volume of air that is exchanged per respiration. Gurgling sounds often accompany panting. Their breathing sounds labroured and gaspy, and they may be crouching and have ruffled feathers. Birds may also die without any obvious symptoms. the abdomen of ascitic birds is often dilated (enlarged) because of ascitic fluid in chickens that have an increased respiration rate and reduced exercise tolerance.

Older birds which are mildly ascitic may show signs of cyanosis (a blue discolouration of the skin) especially around the comb and wattles. Cyanotic birds have been observed to die spontaneouly, especially when excited. Post mortem analyses of ascitic birds indicate that the skin and tissues are congested and they are often a dark red colour. Opening the abdominal cavity of an ascitic bird reveals an amber or

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clear fluid (lymph) that resembles blood plasma. This abdominal fluid is called ascitic fluid. The heart of ascitic birds is enlarged and there is fluid in the pericardium (the sac surrounding the heart). The liver may be edematous (swollen and congested) and may have fibrin (blood clotting protein which is soluble in the blood) adhering to the surface. Blood plasma builds up in the low-pressure liver venous system because it is unable to return to the heart in suficient volume. Classically, the right ventricle (RV) is grossly dilated and can make up as much as 40% of total ventricle weight, compared with the normal 20%. Varying degrees of lung damage are seen. Lungs of ascitic birds often appear pale or grayish. The lungs are extremely congested and edematous.

 

How Ascites results?:

Typically, as mentioned in the flowchart, the series of events that lead to the development of the ascites syndrome begn when broilers first start to gain body weight or muscle mass. The thin right ventricle is prone to becoming distended in response to its increased workload. Increased pulmonary arterial pressure (blood pressure between the heart and the lungs) is due to both an increase in blood flow and increased resistance in blood flow.

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In an attempt to increase the blood's oxygen carrying capacity, red blood cell production is increased. This causes a "thickening" of the blood, and further resistance to blood flow, compounding the lung congestion problem.

As the right ventricle dilates, the valves become increasingly inefficient and allow some blood to flow back into the atrium. This leads to right ventricular failure. The increase in back flow causes liver congestion (edema) because the capillaries cannot exchange the fluid and the high pressure causes the plasma to lead from the liver and capillary beds into the body cavity.

 

Management practices to prevent Ascites:

Feed Restriction

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Reducing the feed intake of broilers decreases the growth performance. Feed restriction is only of economic benefit when the incidence of ascites is very severe.

From a metabolic point of view, the first three weeks of life are an especially stressful period for a broiler. Muscle and bone growth, as a percentage of body weight, is greatest during this time. Slower growing birds have reduced oxygen needs. Feed restriction slows body growth, allowing the cardiopulmonary organs (heart and lungs) to keep up with the oxygen demands of the birds.

Feed restriction during the finishing period is less important because the weight gain relative to frame size is less. Birds which are feed restricted early may be able to enter the grower and finisher periods with stronger cardiopulmonary systems. With moderate feed restriction, the birds may be able to achieve similar weights to non-restricted birds. With a smaller frame size, there is less feed required for maintenance, and overall feed conversion efficiency is improved through compensatory growth.

 

Feed form Mash Vs Pellets:

Reducing the intake of nutrients can reduce the incidence of ascites. Pelleted feed is more nutrient dense, and allows birds to increase nutrient intake. Mash feed can be fed during the starter period (from day 0 to 21 or 28 days of age) to reduce ascites. When fed in the first 4 week mash feed reduced mortality without downgrading market parameters.

Composition of the feed (nutrient reduction programs)

Qualitative feed restriction can be achieved by lowering the energy content of the diet. If this is done early in life, when feed intake per unit of metabolic weight is at its highest. Oxygen requirement are reduced and therefore susceptibility to ascites is also reduced. It has also been suggested that dietary compositions that improve feed conversion rtio also increse the incidence of ascites. These factors include high energy density, a high protein:energy ratio, and pelleted diets.

Lighting programs are a method of restricting feed intake by restricting access to feed. Lighting programs have been used to reduce the incidence of leg problems. Sudden Dealth Syndrome (SDS) and ascites. Sudden Death Syndrome in broilers may be related to ascites and can

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occur secondarily to right ventricular failure. It is possible that the step-up lighing program reduces the level of activity compared with continous lighting. These lighting programs reduce the number of hours of light per day that the birds are exposed to (after 5 to 7 days of age). Programs which work well commercially reduce the light from 24 hours / day to 6-8 hours / day, followed by weekly increases. For broiler chickens these increases are approximately 4 hours more light each week.

Feed restriction can be an effective means of reducing the incidence of ascites, but it must be used in conjunction with good management. Once optimal management practices have been ensured, restricted feeding can be highly effective in further reducing the incidence of ascites in commercial broiler flocks.

All the reseach has found that reduced environmental oxygen following hatching results in irreversible pulmoary hypertension and development of ascites. Ascites has thus been shown to be associated with both rapid growth rate and low environmental oxygen resulting from poor ventilation, litter ammonia and / or dust. Higher salt intake is yet other factor. Management of ascites should address these issues in totality.

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