poultry health ascites

The ascites syndrome in broiler flocks has been increasing at an alarming rate, and this condition has become one of the leading causes of mortality and whole carcass condemnations throughout the world. Ascites represents a spectrum of physiological and metabolic changes leading to the excess accumulation of fluid in abdominal cavity. These changes occur in response to a number of dietary, environmental and genetic factors. Improvements in growth performance and decreases in mortality rates, as well as benefits in alleviating ascites have been observed in recent trials with BIOMIN's acidifier product Biotronic^® SE.


Definition:

The term "ascites" actually refers to the fluid accumulation in abdominal cavity (or so called "waterbelly"). The disease is more scientifically known as pulmonary hypertension syndrome. Ascites is most commonly diagnosed at 4 - 5 weeks of age. Total mortality due to ascites is higher in the male parent lines, which have the capability of faster growth and higher muscle deposition compared to the female lines (Dewil et al., 1996).


Pathology:

The pathology is associated with abnormally high blood pressure between the heart and lungs (pulmonary hypertension) leading to heart failure, increased blood pressure in the veins, and excessive build-up of fluid in the liver which leaks into body cavity (Maxwell, 1990).


Characteristic symptoms:

• Poor bird development
• Dilated abdomen ("waterbelly")
• Dyspnoea (panting, accompanied with gurgling sounds, even in the absence of apparent heat stress)
• Possible cyanosis (a blue discolouration of the skin, especially around the comb and wattles and muscle tissue (Figure 1)).

Figure 1. The ascitic (upper) and normal (lower) breast muscle of broiler


Aetiology:

The aetiology of ascites is very conflicting. Usually genetics have been blamed for the ascites. However, the breeding companies have improved genetic resistance of the stock to the ascites. The combination of environmental (ambient temperatures, high altitudes, stock density, air quality), nutritional (diet density, feeding type), hygienic (feed, environmental hygiene) and genetic events lead to this metabolic disease.

A considerable number of ascites syndrome in broiler flocks is caused by microorganisms. Most of the Gram-negative bacteria (E. coli, Salmonella sp., Campylobacter) are considered pathogenic because of their lipopolysaccharide (LPS) layer. Some studies have shown that LPS triggers pulmonary vasoconstriction leading to ascites (pulmonary hypertension) in broilers (Chapman et al., 2005). Airborne LPS is ubiquitous in the environment of broilers, and is positively related to the amount of organic dust in poultry houses (Zucker et al., 2000). For example, respiratory exposure to E. coli can amplify the incidence of ascites five-fold in broilers. It is known that Salmonella typhiumurium may cause up to 79% mortality in one week old chickens. However, in some studies lesions of salmonellosis were reported for 4 to 6 week old broilers with E. coli co-infection consequentially leading to ascites (Ganapathy et al., 2000).

Another pathogenic agent is a mould, Aspergillus fumigates, occasionally present in the environment of all poultry. Disease caused by this mould, so called "brooder pneumonia", forms mould colonies in the lungs, and produces hard nodular areas leading to air sac infection and subsequently to the development of ascites.


Treatment and prevention of ascites:

Firstly, it is important to understand the underlying causes of an ascites occurrence on a poultry farm. In the case of ascites caused by genetics, feed restriction might reduce the effect of the disease. Slower growing birds have reduced oxygen needs allowing the cardiopulmonary organs (heart and lungs) to keep up with oxygen demands of the birds. However, 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.

In the case of ascites caused by microorganisms, recent studies investigating the effect of feed supplementation with acidifiers have shown promising results. Of course, optimal management practices are also very important for reducing the problem of ascites and maximising performance of broilers.



The effect of the acidifier Biotronic^® SE on ascites incidence on a commercial broiler farm (Bolivia)


Trial design.  Nine hundred day-old Cobb 500 male broiler chicks were divided into three groups. The birds were fed a corn-soybean meal diet. The Negative control group diet contained no feed additives, whereas the diet of the Positive control group was supplemented with an antibiotic growth promoter (AGP), and the trial group was supplemented with the acidifier Biotronic^® SE (BIOMIN GmbH) at an inclusion rate of 1.5 kg/t feed. The duration of the trial was 46 days. The weight of the birds was recorded on days 14, 35, 42 and 46. Mortality and observations of the birds for abnormalities (diarrhea, depression, immobility) were carried out daily.


Farm management.  The trial was conducted on a commercial broiler farm 2600 metres above sea level in Bolivia. The mean external ambient temperature was 18°C, and the humidity was 40%. The birds were vaccinated against Newcastle, Infectious Bronchitis and Infectious Bursal disease.


Ascites incidence.  Ascites incidence was characterized by clinical signs (panting, gurgling sounds, cyanotic combs and wattles, excessive abdominal fluid accumulation) and mortality rates. The incidence of ascites was confirmed by postmortem examination.


Results and Discussion.  For the initial 42 days, the broilers did not show any obvious clinical signs of ascites, even though on Day 35 mortality rates were recorded in the Negative control, Positive control and Biotronic^® SE groups as 2.04, 3.09 and 2.39% respectively (Table 1). On Day 42 an outbreak of ascites was observed on the broiler farm with typical ascitic symptoms such as gasping, cyanotic combs and wattles, depression, extended abdomens, and increased mortality rates up to 7.53, 5.26 and 3.81% in the Negative control, Positive control and Biotronic^® SE groups respectively. In the Biotronic^® SE group, the mortality rate increased 37.27% over the mortality rate prior to the ascites outbreak, compared to 72.90 and 41.25% respectively in the Negative control and Positive control groups.


Table 1.Effect of Biotronic^® SE on body weight and mortality rate in broilers