Intestinal diseases are an important concern for modern poultry industry because of low productivity, increased mortality, reduced welfare and the associated contamination of poultry products with pathogenic bacteria and their toxins.
Several pathogens (Viruses, bacteria and parasites) are incriminated as possible causes of enteric disorders either alone (mono-casual), in synergy with different other micro organisms (multi-casual) or with non-infectious causes such as feed and or management related factors (Table 1)
Necrotic enteritis is one of the world´s most common and financially crippling disease which when triggered can cause mortality rates upto 50%. Necrotic enteritis is an infectious disease caused by Clostridium perfringens which is a nearly ubiquitous gram positive, spore forming extremely prolific, toxigenic anaerobic bacterium. These attributes enable the bacterium to be present almost any time & place with poultry and then proliferate and produce toxins when the circumstances are favorable. It can be found in soil, dust, faeces, feed, poultry litter and at low levels in the intestine of healthy birds. The disease can affect birds at almost any age but primarily affects broiler chicken between 2-5 weeks of age raised on litter. The bacterial spores are very resistant to heat, desiccation, acids and many chemical disinfectants.
Clostridium perfringens is divided into five biotypes (A,B,C,D and E) based on the synthesis of four major lethal toxins as alpha, beta, epsilon and iota. Along with these four major toxins, enterotoxin (CPE) and beta 2(CPB2) toxins produced by Clostridium perfringens are considered as important toxins for enteric diseases. The infections in poultry are mostly caused by C.prefingens type A and to a lesser extent by type C
Although C.prefingens is the main etiological agent of necrotic enteritis, other cofactors which usually precipitate the outbreak includes:
- High dietary levels if viscous grains (Wheat based diets) with animal protein sources (Fishmeal).
- Damage to the intestinal mucosa through prior infection with coccidiosis.
- Infection of birds with salmonellosis
- Increased digestive viscosity due to inclusion of water soluble indigestible non-starch polysaccharides.
- Physical rupture of the gastrointestinal linning by rough litter.
- Intestinal stasis and intestinal distension.
- Rough climatic conditions.
- Improper management.
The clinical signs appear suddenly; apparently healthy birds may become acutely depressed and die within hours. Early signs of disease include wet litter & dark coloured diarrhoea. The birds are depressed with low mobility, poor appetite and ruffled feathers. Mortality ranges from 2 to 10%. In the acute form of disease, birds often die without any clinical signs. However, death seldom occurs in sub-clinical form but erodes performance and is more financially damaging for the producer because of impaired feed efficiency, reduced live weight at slaughter and increased condemnation percentage. The diagnosis of subclinical form relies heavily on the quality and frequency of technical services provided.
On autopsy, dehydration is the most common finding. Breast muscles are dark red and gizzard is full. Severe inflammation the duodenum and jejunum is the most predominant finding but in some instances the entire length of the intestinal tract is involved. The intestine is distended and contain dark offensive fluid. The mucosa is covered with green or brown diptheroid membrane which can be easily separated from the lining. Varying degrees of sloughing of the intestinal mucosa could also be observed (Fig. 1)
A presumptive diagnosis may be made from the case history, clinical signs, lesions and staining fresh smears of upper part of the intestinal tract with gram stain showing an abundant number of clostridial organisms (Fig. 2)
Treatment with antiboitics such as pencillin, amoxicillin, ampicilin, erythromycin, dihydrostreptomycin and tetracycline provides a satisfactory clinical response. Three days is the maximum duration of treatment but longer applications may be required. Administration of dietary Tylan for seven consective days following conformation of a necrotic enteritis field outbreak reduces the mortality and lesion scores.
PREVENTION AND CONTROL MEASURES:
There are several measures that can be taken to control the necrotic enteritis. These include:
- Sound cleaning and disinfection of the environment between flocks to decrease the bacterial load in the shed. Improved management, reduced environmental stress, use of clean litter, enhanced biosecurity and sanitation helps to reduce the incidence of disease.
- Diet should be formulated using high quality, highly digestible ingredients with well-balanced amino acid and nutrient profile.
- Drastic changes in the diet should be avoided.
- Improve digestibility of feed so no undigested feed remains in the bird, thereby becoming a basis for bacterial multiplication.
- Any managemental practice that reduces the incidence of coccidiosis will also reduce the incidence of necrotic enteritis.
- Bird diversity is a critical factor in preventing necrotic enteritis so overcrowding of birds should be avoided.
- Control water quality by using portable water. Water should be properly chlorinated.
- Acidification of water can contribute to a reduction of the number of pathogenic bacteria in the gut.
- It is possible to reduce the aggressiveness of bacteria through the use of antiboitics.
- Use of alternative weapons like plant extracts, essential oils and organic acid are able to reduce the total bacterial counts in the gut.
- Birds should be fed additive like probiotics symbiotics through diet or drinking water which affects the balance of intestinal microflora in a positive way and thus able to control enteric pathogens.
Various predisposing factors cause the clinical and subclinical necrotic enteritis. Controlling these factors will, upto a large extend reduce economic losses. The implementation of several approaches such as improvement in management, feed formulation and limiting exposure to infectious agents through biosecurity, supportive therapy, cleaning and disinfection are essential for control of necrotic enteritis in poultry.