FEED Business Worldwide - August, 2011
Clostridial enteritis : A continuing challenge for the poultry sector
by Dr. KOH Thong Jin, Product Manager, Kemin Agrifoods Asia
Growth retardation around the third week of age associated with impaired intestinal health is a major problem in broiler production, fully recognized by farmers, veterinarians and nutritionists. This problem occurs so frequently that it is no longer considered as a disease by some veterinarians. The pathogen involved is Clostridium perfringens and issues related to it are prevalent in the broiler industry worldwide
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 an 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 macroscopically evident lesions in the small intestines. A typical example of necropsies in the gastro intestinal tract due a Clostridium infection is shown in Figure 1. 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 poultry age (Figure 2). Litter quality changes and becomes more wet, leading to moisture levels above 40% and often undigested feed particles are found in the litter (Figure 3). 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.
The causative bacteria
Clostridium perfringens is an organism commonly found in the intestinal tract of poultry, colonizing in the early phase of a bird's life. 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 their environment, usually from such sources 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.
Occurrence 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 diagnosed1 (Figure 3). A follow-up study in 2005 indicated an increased incidence of Clostridial enteritis in all regions of the world. Recent European surveys confirmed the severity and the widespread of the problem2.
Impact of Clostridium on animal performance
Clostridium perfringens associated necrotic enteritis may appear with variable degrees of severity. An overview of the impact of Clostridium on broiler performance is summarized in 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 is known as a serious profit killer, leading the FCR to increase with 6â€“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 economy. Annual losses to producers in the U.S. 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.1
Predisposing factors leading to necrotic enteritis
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 also very important in order to control the actions of Clostridium. Diets with high levels of indigestible, water soluble non starch polysaccharides (eg 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 and its growth is therefore enhanced in an environment rich with proteins.
Besides these factors, several other nutritional factors influence 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 will results 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 so 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.
In general, any factor that stresses the broiler chicken's 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 in the disease onset. When a watery intestinal content and wet litter are observed Clostridium that have already had a chance to proliferate.
The traditional method of managing Clostridial enteritis has been through the use of antibiotics growth promoters (AGPs). Preventive action through products with selected activity against Clostridium perfringens before the first symptoms are observed are a valuable solution to the maintaining of healthy poultry gut flora.
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