Healthy gut is key in targeting NE

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.