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Healthy gut is key in targeting NE

Necrotic enteristis (NE) associated with clostridium perfringens is a complex disease affecting most poultry, especially broilers. NE is one of the major challenges in poultry production today and requires creative strategies for control. A key factor in prevention is maintenance of the integrity of the gut wall. Probiotics help by reducing the number of clostridium perfringes and other enteropathogens, and contribute to efficient digestion.

By Dr Elinor McCartney 
 
In 1984, necrotic enteritis (NE) was considered as an uncommon disease in poultry with minor economic loss. Surveys in 2006 placed NE in the top 5 poultry diseases, costing the world poultry industry around US$40 billion (€29.9 billion). Sub-clinical NE adds 5 cents to the production cost of every broiler. Many industry specialists believe that the EU ban on AGPs (antibiotic growth promoters) and the increasing pressure against the use of all antimicrobials in animal feeds will make the control of NE an impossible task, but this view may be an over-simplification. During the 1980s and 1990s, the NE problem increased significantly, despite the fact that antimicrobial use also increased dramatically over the same period. Resistance to both antibiotics and anticoccidials has undoubtedly contributed to the increasing prevalence of NE over the past 25 years.
 
Complexity of NE
NE is a complex disease and the lesions are always associated with Clostridium perfringens, but many factors may contribute. Experts agree that the risk of NE is higher when birds suffer intestinal damage, classically but not exclusively due to coccidiosis, and when the intestinal flora is disrupted (Figure 1). NE tends to be seen in broilers at 2-5 weeks of age, in turkeys at 4-10 weeks of age and in pullets at 12-16 weeks of age. This is because coccidiosis also attacks at these ages, causing gut wall damage, and allowing opportunistic infection by Clostridium perfringens. Figure 2 illustrates typical lesions of NE in the chicken gut.
 
No “silver bullet”
Researchers studying NE agree that there is no single product or technology that will solve the problem. There is no “silver bullet” for NE. Poultry farm managers need to select and combine control measures that are best suited to each production situation. Table 1 summarises the main factors influencing the incidence and severity of NE, and comments on strategies for control.
Contribution of bacillary probiotics Bacillary probiotics are one of many tools that can combat NE, particularly the insidious sub-clinical form. Bacillary-based products have the advantage of good stability in pelleted feeds. One strain (Bacillus subtilis C-3102* - Figure 3), is approved for use in all the main poultry-producing areas of the world, including the EU, USA, Latin-America and Asia. Experience and recent research illustrates how bacillary probiotics can help fight NE and contribute to improved performance.
 
Broilers
Japanese field trials published in 1996 demonstrated that bacillary probiotics can reduce enteric pathogens, including Clostridium perfringens. Table 2 illustrates that including a bacillary probiotic in feed not only reduces the numbers of intestinal Clostridium perfringens, but also halves the detection rate. In addition, the number of birds positive for Salmonella
is significantly reduced. The positive effect on the intestinal environment is translated into better broiler performance. EU research trials in broilers produced without AGPs or antibiotics showed that growth and feed efficiency improved by around 3%.
 
Layers and breeders
Bacillary probiotics are useful in layer nutrition, especially in the latter half of the laying cycle where they improve egg-shell strength. This improvement is thought to be due to better calcium utilisation related to higher lactic acid production from lactobacilli. The stimulating effect of Bacillus subtilis C-3102 on lactobacilli is invariably associated with lower numbers of enteropathogens, including Clostridium perfringens. Field trials carried out under commercial conditions in layers and breeders showed that in the layers the percentage of lactobacilli in the flora increased from 54 to 74%. In the breeders, where NE was a problem, supplementation with Bacillus subtilis C-3102 resulted in a significant reduction in Clostridium perfringens and a significant increase in lactobacilli. In addition, the detection rate of Clostridium perfringens fell from 100 to 60% of sampled birds.
 
Strategic application
Successful use of bacillary probiotics to aid in controlling NE requires good understanding of the selected probiotic and the NE threat. Bacillus subtilis C-3102 is compatible with a wide range of antibiotics, coccidiostats and other feed additives, and can be used flexibly in many types of NE control programmes. In general, probiotics are probably best used continuously in order to reduce the risk of NE, with higher application rates on problem farms and during high-risk periods, such as the wet winter months. Higher application rates are advisable over the age range when coccidioisis is likely to occur, starting just before coccidial attacks are likely. Further research and field experience will help to elucidate if synergies with veterinary antibiotics, AGPs (where permitted) and AGPAs can eliminate the challenge of necrotic enteritis.
 
*Bacillus subtilis C-3102 (Calsporin®, Calpis Co. Ltd.) got EU approval in 2006.
 
Source: Feed Mix Magazine Vol. 15 nr. 2

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