Despite investigation of the ascites syndrome for many years, it is still a condition that inflicts financial loss on poultry farmers around the world. It is estimated that 5% of the 40 billion broilers produced annually around the world, as well as 20% of roaster birds, die of ascites.
The incidence of ascites has been increasing in recent years. According to an annual survey in the United Kingdom, broiler producers reported 88 million and 130 million death cases due to ascites in 2005 and 2006 respectively. The cost to the broiler industry of ascites-related condemnation of chicken carcasses at processing reached $2.25 million in 2003. The cost to the worldwide broiler industry due to ascites-related mortality has been estimated to be in excess of $500 billion per year. The question is, how can ascites be minimized?
Ascites represents a spectrum of physiological and metabolic changes leading to the excess accumulation of fluid in the abdominal cavity. These changes occur in response to a number of dietary, environmental and genetic factors.
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 the body cavity.
Environment, nutrition contribute
Traditionally, genetics has been blamed for ascites in bird flocks. However, breeding companies have improved genetic resistance of stock to this syndrome. In reality, a considerable number of ascites occurrences are triggered by microbial factors (E. coli, Salmonella sp., Aspergillus) coupled with contributing environmental and nutritional factors.
With genetic resistance to the disease improved, a considerable number of ascites syndrome in broiler flocks is likely caused by microorganisms.
Acidifiers have gained considerable attention in modern animal production as an efficient alternative to antibiotics. Dietary acidification with organic acids has been shown to contribute to environmental hygiene by preventing feed and water from microbial and fungal deterioration. Moreover, dietary supplementation with acidifiers decreases the occurrence of pathogenic bacteria in the gastrointestinal tract, thus improving animals' growth performance and health status. It is also proven that acidifiers successfully fight against gastrointestinal pathogens. With promising results in the alleviation of ascites in broilers, the application of acidifiers can be further expanded.
Treatment and prevention of ascites
First, it is important to understand the underlying causes of an ascites occurrence in 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. In the case of ascites caused by microorganisms, recent studies with acidifiers have shown promising results. Of course, optimal management practices are also very important.
A trial using an acidifier on a commercial broiler farm in Bolivia demonstrates the impact dietary acidification can have on ascites incidence.
Trial design and farm management
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 while the diet of the positive control group was supplemented with an antibiotic growth promoter (AGP). The trial group was supplemented with an acidifier (Biotronic SE, BIOMIN GmbH) at 1.5 kilogram/metric ton 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.
The trial was conducted on a commercial broiler farm 2,600 metres above sea level in Bolivia. The mean external ambient temperature was 18C and the humidity was 40%. The birds were vaccinated against Newcastle, infectious bronchitis and infectious bursal disease. Ascites incidence was characterized by clinical signs and mortality rates. The incidence of ascites was confirmed by post-mortem examination.
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 acidifier groups as 2.04%, 3.09% and 2.39% respectively (see Table). 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. Mortality rates increased up to 7.53%, 5.26% and 3.81% in the negative control, positive control and acidifier groups respectively.
In the acidifier 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. Necropsy of the dead birds revealed the characteristic lesions of ascites. Amber or clear fluid (lymph) was found in the abdominal cavity, hearts were enlarged with fluid in the pericardium (the sac surrounding the heart), livers were swollen and congested and sometimes with fibrin adhered to their surface, and lungs were pale or grayish.
By the end of week seven, the mortality in the negative control and positive control groups reached 15.39% and 7.53%, respectively, whereas the group fed diets supplemented with the acidifier recorded the lowest mortality rate at 6.76%.
This trial result demonstrated that diet supplementation with this acidifier represents a solution to alleviate the effect of ascites. In this study, ascites could be attributed to a microbial cause, most probably Salmonella sp. or E. coli, and some other co-infection agents.
The genetic cause of ascites herein might be excluded, since the growth of the broilers was much lower compared with the standard growth performance of Cobb 500. Due to poor hygienic conditions on the farm, conditions for the proliferation of pathogenic microorganisms in the environment and feed were favorable. Moreover, some predisposing factors such as high altitude and insufficient ventilation were present.
Because of its anti-microbial effect, the acidifier used in the trial improved the environmental hygiene and prevented the feed from microbial and fungal deterioration. In addition, dietary supplementation with acidifiers is known to decrease the occurrence of pathogenic bacteria in the gastrointestinal tract, thus improving the animals' health status. This was confirmed by the reduction of mortality rates in the acidifier group compared with the negative control and positive control AGP groups.
In modern animal production, acidifiers have been proven to be an efficient alternative to antibiotics. Dietary acidification contributes to environmental hygiene, with a continued function through either the feed or water into the animals' gastrointestinal tract. The acidifier used in the above-mentioned trial has been successful in alleviating the effects of various intestinal diseases, with its action against ascites in broilers the latest application available to producers.