Introduction: Poultry meat and egg production have shown considerable increase over the last 30 years. In addition to the enormous growth of the industry, commercial poultry is genetically selected for ever increasing growth and performance. Now days 1.50 Feed Conversion Ratio ( FCR ) is possible for 2 kg live body weight in 33 days which was 1.80 FCR in 40 days for the same body weight 10 years before. This achievement is mainly due to advancement of nutrition, better management practices and disease control programs. But this achievement, apart from the above developments, directly related to gut health which in turn healthy balanced microflora. To meet the modern production standards and maintain the excellent feed efficiency, poultry must have a healthy and functional gastrointestinal tract (Porter, 1998). In the body, the gastrointestinal tract has the most extensive surface and it is constantly exposed to a wide variety of potentially harmful substances (Yegani and Korver, 2008). A variety of enteric bacterial infections poses a serious threat to gastrointestinal health and overall flock performance. Among the bacterial infections, Necrotic Enteritis (NE), is caused by Clostridium perfringens and is a serious disease which can cause significant mortality and morbidity. The Clostridium perfringens infections may occur in acute form with increased mortality and subclinical form with reduced performance like decreased digestion and absorption, reduced weight gain, increased FCR (Yegani and Korver, 2008).
Development of GI tract and gut microflora
The gastrointestinal tract is poorly developed in first days of chicken life. During the first few days, the GI tract continues to grow and the villi size and mass increase significantly. The villi in duodenum develop by 4-5 days of age and in the jejunum and ilium by 10 -12 days of age (Bains, 2003). The small intestine of newly hatched chick undergoes morphological, biochemical and molecular changes during 2 weeks of post hatch and most dramatic changes occur within first 24 hours post hatch (Yegani and Korver, 2008).The development of GI tract, secretion of enzymes and development of gut associated lymphoid tissue are closely correlated with initiation of feed intake after hatch (Bains, 2003).
At hatch the GI tract is sterile and the early post hatch period is critical for establishment of the gut microbial community. The composition of microflora changes with age, breed, diet, geographic location, antibiotic administration and infection with pathogens (Lu et al., 2003; Yegani and Korver, 2008). The small intestinal microflora of adult birds is established within 2 weeks of hatching and the adult caecal microflora, mainly obligatory anaerobes, required up to 30 days to establish (Lee et al., 2010). The adult GIT microflora is composed of 107 to 1011 bacteria per gram of contents (Apajalahti et al., 2004). There is also significant diversity among microbial population in different parts of GI tract and the population tends to increase proximal to distal part (Yegani and Korver, 2008). The Lactobacilli population is predominant in small intestine and Clostridium population is predominant in caecum (Lu et al., 2003). A close relationship exists between the development of normal intestinal microbial population and resistance against enteric pathogens. The gut microflora plays a critical role in maintaining homeostasis which is essential for maintaining the animal health (Lee et al., 2010).
Necrotic enteritis has been reported in most parts of world where poultry are produced. It was first described by Parish in 1961 (Long et al, 1974) and the incidence of NE has increased significantly in commercial broiler flocks over the last few years in every region of the world (Bains, 2003). NE is reported in many bird species. Among chickens the disease is most common in broilers, but out breaks in pullets and adult layer chicken has also been reported. Rapidly growing young chicken, especially 3 to 12 weeks of age, are most susceptible (Kaldhusdal and Lovland, 2002). The disease characterized by damage to the intestinal mucosa by toxins produced by the causative bacteria (Aziz and Barnes, 2011). It has been estimated that the cost of sub clinical NE can be as much as US$ 0.05 per bird and both forms of the disease (clinical and sub clinical) may be causing US$ 2 billion in losses to the world poultry industry annually (Van der Sluis, 2000)
The causative bacteria and Pathogenesis:
Necrotic enteritis is caused by Clostridium perfringens, a gram positive, rod shaped, spore forming, and anaerobic bacterium. The bacteria can be found in soil, dust, feces, feed, litter and intestinal contents (Dahiya et al., 2005). C. perfringens grow in pH range 5-8 and their spores are most resistant biological cell type. They can survive under extreme conditions, resisting heat, desiccation, acids and many chemical disinfectants (Johansson, 2006). C. perfringens is divided in to five toxinotypes (A, B, C, D and E) based on four major toxins namely alpha, beta, epsilon and iota (Aziz and Barnes, 2011). Alpha toxin produced by C. perfringens type A and C and beta toxin produced by C. perfringens type C are believed responsible for intestinal mucosal necrosis, the characteristic lesion of NE (Opengart, 2003). Among this the majority of isolates of NE cases are type A and few cases are type C (Aziz and Barnes, 2011).
Alpha toxin produced by type A bacteria is the important virulent factor for the disease. Alpha toxin is a zinc-metalloenzyme phospholipase that hydrolyses phospholipids in membranes of blood cells, endothelial cells and muscle cells. Because of its hydrolytic property, the toxin is hemolytic, cytotoxic, necrotizing, and potentially lethal (Songer, 1996). Toxins absorbed from the intestinal tract produces toxemia which is responsible for death. In addition to Alpha toxin, recently another toxin netB has been identified in certain strains of C. perfringens that were isolated from chicken suffering from NE. This toxin is thought to be a major virulence factor for NE (Keyburn et al., 2008). But the recent studies revealed that netB toxin cannot be the only C. perfringens virulence factor, since not all C. perfringens isolates from birds associated with NE contain the gene for netB toxin (Tolooe et al., 2011).
The development of liver lesions is poorly understood. Both bacteria and toxin may be transported through damaged gut mucosa to the liver by blood. An ascending infection via the bile tree, and the inflammatory processes obstructing the bile flow, are the other possibilities (Kaldhusdal and Lovland, 2002).
Clostridium perfringens is found in the intestinal tract of healthy chickens, usually in small numbers (<=104 CFU/g of digesta) and is spread through feces in production units and intestinal rupture in processing plants (Dahiya et al., 2007). But disturbances in normal intestinal microflora may cause rapid proliferation of C. perfringens and increasing bacterial numbers to 107 to 109 CFU/g of digesta resulting in the development of subclinical or clinical NE (Dahiya et al., 2005). But the events leading to this excessive growth, subsequent toxin production and mucosal damage are poorly understood (Songer, 1996). However, certain factors predispose the birds to NE. These factors can be divided in three major categories.
However there is probably other predisposing factors causing NE yet to be identified
Clinical signs and lesions.
The clinical form of NE is characterized by depression, ruffled feathers, decreased appetite, reluctant to move and diarrhea. The duration of clinical signs may be very short and sudden death occurs commonly with no premonitory signs. Gross and microscopic lesions are usually confined to the small intestine, primarily jejunum and ileum; however, caecal lesions are also described. Intestines are often friable and distended with gas. The mucosa is lined by a loosely or tightly adherent yellow or green pseudomembrane usually with little hemorrhage (Opengart, 2003).
An important characteristic of the disease is the subclinical form which does not result in mortality but is associated with poor performance. Impaired feed conversion, reduced growth rate and increased condemnation rates are the major production losses due to sub clinical NE (Lovland and Kaldhusdal, 2001). Mild focal ulceration can be found in small intestine and these ulcers are equivalent to the areas of mucosal necrosis seen in clinical NE, but are smaller in range of 1 -5 mm diameter. These focal ulcers result in localized fluid loss and failure of nutrient absorption as well as absorption of tissue necrosis products. This would account for depressed growth and feed intake along with the common sign of diarrhea (Wilson et al., 2005). The subclinical form of the disease can be graded according to the severity.
When the birds are suspected for NE, it is best to examine euthanized or fresh dead birds for lesions. Once the intestine starts decompose after death, NE lesions tend to be less obvious (Aziz and Barnes, 2011).
Diagnosis of NE can be made based on typical gross and microscopic lesions and isolation of the causative agent. In field cases C. perfringens can be readily isolated from intestinal contents or scrapings from intestinal wall by anaerobic incubation overnight at 37oC in blood agar plates (Opengart, 2003). Clostridium enumeration can be done from fresh intestinal contents using sterile peptone buffer followed by serial dilution in peptone water and incubated anaerobically in blood agar plates (Dahiya et al., 2005). The samples should be sent to laboratory as soon as possible for enumeration or isolation. The results of bacterial culture need to be interpreted in the context of clinical history, gross lesions, and preferably microscopic lesions (Aziz and Barnes, 2011).
As we know the GI tract of the birds contain several bacteria that compete with each other in the intestinal environment and NE occurs when C. perfringens overgrow in the intestinal tract. Keeping the GI tract microflora healthy and balanced are key factors for prevention of NE. Supplementing some beneficial microorganisms to birds is effective in preventing NE. Lactobacilli Sp and Bacillus Sp are widely used as for this purpose. There are several criteria for selection of these microorganisms which are called direct-fed microbial (DFM) which may assist in the prevention of NE. These organisms should fulfill the following important criteria (Kabir, 2009).
Supplementing birds with Bacillus subtilis PB6 (CLOSTATTM) organisms helps to maintain the gastrointestinal tract healthy and balanced. These organisms are derived from healthy chicken intestine, and resist pelleting conditions and the pH of the GI tract. Most of the probiotics, such as Lactobacilli, eliminates the pathogens by the mechanism of competitive exclusion (Lee et al., 2010). CLOSTATTM has unique features of controlling the Clostridium perfringens by secreting secondary metabolites. CLOSTATTM has beneficial effects on the intestinal health of chickens by encouraging the growth of beneficial bacteria and reducing the population of Clostridium perfringens.
Balancing the intestinal microflora by supplementing with active microbials like CLOSTATTM assists in preventing the occurrence of NE, thus preventing the economic loss.
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Apajalahti J, Kettunen A and Graham H. 2004. Characteristics of the gastrointestinal microbial communities with special reference to the chicken. World’s Poultry Science Journal 60, 223-232
Aziz T and Barnes J, 2011. Balanced intestinal microflora help prevent necrotic enteritis. World Poultry 27, 30-32
Bains B.S. 2003. Challenges to the gastrointestinal integrity in commercial broilers. World Poultry 19:12, 17-19.
Dahiya J.P, Hoehler D, Van Kessel A.G and Drew M.D. 2007. Effect of different methionine sources on intestinal microbial populations in broiler chickens. Poultry Science, 86, 2358-2366.
Dahiya J.P, Hoehler D, Wilkie D.C, Van Kessel A.G and Drew M.D. 2005. Dietary glycine concentration affects intestinal Clostridium pefringens and Lactobacilli populations in broiler chickens. Poultry Science, 84, 1875-1885.
Drew M.D, Syed N.A, Goldade B.G, Laarveld B, and Van Kessel A.G. 2004. Effects of dietary protein source and level on intestinal populations of Clostridium perfringens in broiler chickens. Poultry Science, 83, 414-420
Immerseel F V, Buck J D, Pasmans F, Huyghebaert G, Haesebrouck F and Ducatelle R. 2004. Clostridium perfringens in poultry: an emerging threat for animal and public health. Avian Pathology, 33:6, 537-549.
Johansson A. 2006. Clostridium perfringens the causal agent for necrotic enteritis in poultry. Doctoral thesis.
Kabir S.M.L, 2009. The role of probiotics in the poultry industry. International Journal of Molecular Sciences. 10, 3531-3546
Kaldhusdal M and Lovland A. 2002. Clostridial Necrotic Enteritis and Cholangiohepatitis. In: The Elanco Global Enteritis Symposium, Norway.
Keyburn A.L, Boyce J.D, Vaz P, Bannam T.L, Ford M.E, Parker D, Di Rubbo A, Rood J.I, Moore R.J. 2008. NetB, a new toxin that is associated with avian necrotic enteritis caused by Clostridium perfringens. PLOS Pathogens 4, e26.
Knarreborg A, Simon M.A, Engberg R.M, Jensen B.B, and Tannock G.W. 2002. Effects of dietary fat source and sub therapeutic levels of antibiotic on the bacterial community in the ileum of broiler chickens at various ages. Applied and Environmental Microbiology, 68:12, 5918-5924.
Lee K, Lillehoj H.S and Siragusa G.R. 2010. Direct-Fed Microbials and Their Impact on the Intestinal Microflora and Immune System of Chicken. Journal of Poultry Science 47, 106-114.
Long J.R, Pettit J. R and Barnum D.A. 1974. Necrotic Enteritis in Broiler Chickens II. Pathology and Proposed Pathogenesis. Can. J. Comp. Med 38, 467-474 Lovland A and kaldhusdal M. 2001. Severely impaired production performance in broiler flocks with high incidence of Clostridium perfringens associated hepatitis. Avian Pathology 30, 73-81
Lu J, Idris U, Harmon B, Hofacre C, Maurer J.J and Lee M.D. 2003. Diversity and Succession of the Intestinal Bacterial Community of the Maturing Broiler Chicken. Applied and Environmental Microbiology 69:11, 6816-6824.
Opengart K . 2003. Necrotic Enteritis . Diseases of Poultry edited by Y.M.Saif, 11th edition. 781-784
Porter R.E. 1998. Bacterial Enteritides of Poultry. Poultry Science 77, 1159-1165.
Songer J.G. 1996. Clostridial enteric diseases of domestic animals. Clinical Microbiology Reviews 9, 216-234
Tolooe A, Shojadoost B, Pieghambari S.M and Tamaddon Y. 2011. Prevalence of netB gene among Clostridium perfringens isolates obtained from healthy and diseased chickens. Journal of Animal and Veterinary Advances 10:1, 106-110.
Van der Sluis W. 2000. Clostridial Enteritis is an often underestimated problem. World Poultry 16, 42-43
Wilson J, Tice G, Brash M.L, and Hilaire S.St. 2005. Manifestations of Clostridium perfringens and related bacterial Enteritides in broiler chickens. World Poultry Science Journal, 61
Yegani M and Korver D.R. 2008. Factors Affecting Intestinal Health in Poultry. Poultry Science 87, 2052-63.