Clostridial enteritis affects intestinal health in broiler flocks and may cause considerable losses. It is caused by Clostridium perfringens and is found all over the world. Fighting the disease is a continuing challenge for the poultry sector. Preventive actions using dedicated products are a valuable solution to maintain healthy gut flora.
By Dr. Tom Verleyen, Kemin Agrifoods Europe, Herentals, Belgium
Growth retardation around the third week of age associated with impaired intestinal health is a major problem in broiler production, fully recognised by farmers, veterinarians and nutritionists. This problem occurs so frequently that it is no longer considered as a disease by some veterinarians. Issues of Clostridial enteritis are prevalent in the broiler industry worldwide. The pathogen involved is Clostridium perfringens.
Manifestation of necrotic enteritis
Clostridium perfringens infections in poultry may show up as an acute clinical infection or by a subclinical infection. The acute form of the disease leads to increased mortality of the broiler flock, which can account for high losses of up to 1% per day, reaching mortality rates up to 50%. Clinical signs include depression, ruffled feathers, diarrhoea and evident macroscopically lesions in the small intestines. The clinical form of necrotic enteritis is easily detected and luckily occurs quite seldom in flocks and can be treated. In the subclinical form of the disease, damage to the intestinal mucosa caused by Clostridium perfringens leads to decreased digestion and absorption of nutrients, reduced weight gain and increased feed conversion. The subclinical form of necrotic enteritis is the most important as it occurs predominantly and has most significant economic impact due to impaired growth rate and feed conversion.
Typical signs seen by poultry producers are specific growth retardation around the 23rd day of age (Figure 1). Litter quality changes and becomes more wet, leading to moisture levels above 40% and often undigested feed particles are found in the litter. Consequences of poor litter quality are obvious, as it leads to increased issues of foot pad lesions, hock lesions and breast blisters resulting in higher levels condemnations at the processing plant.
Causative bacteria, occurrence
Clostridium perfringens is a commensal organism in the intestinal tract of poultry, colonising in the early phase of life of the animals. It is a gram positive anaerobic spore forming bacterium, able to produce various toxins and enzymes responsible for the associated lesions. Clostridium can be classified in five types (A, B, C, D and E), with type A being the most predominant cause of Clostridium infections in poultry. For a long time it was accepted that the alfa toxin is responsible factor, but new research indicates that Net B is related to the causative form of necrotic enteritis.
Chickens generally take up Clostridium perfringens from the environment, such as feed, water, soil etc. Inoculation of animals with Clostridium perfringens does not lead per se to the development of necrotic enteritis. One or several predisposing factors may be required to elicit the clinical signs and lesions of necrotic enteritis.
Studies showed that the subclinical form of necrotic enteritis is a worldwide problem with an average of 80% of the flocks having had Clostridium diagnosed (Figure 2). A follow-up study in 2005 indicated an increased incidence of Clostridial enteritis in all regions of the world. Recent European surveys have confirmed the severity and the widespread of the problem.
Impact on animal performance
Clostridium perfringens associated necrotic enteritis may appear with variable degrees of severity (Table 1). Birds acutely infected with Clostridium perfrigens will show high mortality rates up to 30% of the flock. The clinical form of Clostridium perfringens is easily seen and can quickly be treated through medication. However, as the disease occurs at subclinical level, where mortality is not substantially increased but with clear signs of intestinal disorders, then it becomes more difficult to quantify the impact. At subclinical level, Clostridium perfringens are known as a serious profit killer, leading the FCR to increase with 6–9 points and final body weight to reduce between 3-5%. As subclinical necrotic enteritis is not always detected in the broiler flock there is a serious risk that it can pass unnoticed and affect broiler production. Annual losses to producers in the US and Canada due to subclinical necrotic enteritis are estimated to be $1.5 up to 5 cent per bird, according to a study reported in World Poultry in 2000.
There are several predisposing factors that producers need to be aware of and continuously monitor and try improve on. These are namely infectious causes, nutritional factors, and preventative measure.
The most important known predisposing factor is intestinal damage caused by coccidial pathogens. Intestinal damage by Eimeria results in initial damage of the gastro intestinal lining, which is further used by Clostridium perfringens for additional proliferation. Coccidiosis is often seen to occur just prior to or during a necrotic enteritis outbreak. Inflammation of the gastro intestinal tract or a disruption of the gastro intestinal balance due to an infection often leads to the development of Clostridium perfringens.
Dietary factors are very important in order to control the actions of Clostridium. Diets with high levels of indigestible, water-soluble non-starch polysaccharides (e.g. coming from rye and wheat) are known to increase the viscosity of the intestinal content, which encourages the development of necrotic enteritis. Also diets rich in high levels of proteins such as fish meal give an excellent amino acid source to Clostridium, which is known as a predisposing factor.
As Clostridium lacks the ability to produce 13 out of the 20 essential amino acids, its growth is therefore enhanced in an environment rich with proteins. Besides these factors, several other nutritional factors have an influence on necrotic enteritis. Basically, all diets with an imbalanced nutritional content can predispose necrotic enteritis. Diets with a low energy to protein ratio lead to a higher feed consumption and will result in an excessive protein intake and thereby increase the nitrogen level in the digesta and excreta. Similarly, poorly digested proteins in the lower gastro intestinal tract act as a substrate for the microflora. In order for efficient excretion to take place the animals need to take in larger quantities of water, but then the litter tends to become wetter with a higher level of nitrogen. This allows the opportunity for pathogenic bacteria such as Clostridium perfringens to proliferate in the litter, which is likely to exacerbate the problems. Any factor that stresses the broiler chickens gastro intestinal tract is a risk for Clostridium perfringens proliferation. There is evidence to suggest that alterations in feeding regimes cause stress in the gastro intestinal.
There are clear indications that Clostridial enteritis is under-diagnosed and treated too late. When a watery intestinal content and wet litter are observed, Clostridium already has already proliferated. The traditional method of managing Clostridial enteritis has been through the use of antibiotic growth promoters (AGPs). Preventive actions through products with selected activity against Clostridium perfringens before the first symptoms are observed to be a valuable solution to maintain a healthy gut flora.