Necrotic enteritis is one of the world’s most common and financially crippling poultry diseases affecting approximately 40% of commercial broiler flocks. Clinical outbreaks can cause mortality rates of up to 50% and has been estimated to cost the global broiler industry upwards of $5-6 billion annually. However, it is the sub-clinical form that often goes undetected and thus, untreated.
Necrotic enteritis can lead to a significant effect on performance through its ability to impair nutrient absorption, growth rate, and feed conversion as well as animal welfare, and likely causes a far greater impact on profitability than the clinical disease.
Necrotic enteritis is a result of over proliferation of Clostridium perfringens, a Gram-positive bacteria that is considered a member of the normal intestinal microbiota. Several factors can have a considerable impact on the proliferation of C. perfringens, including management practices, nutritional factors, coccidiosis, and mycotoxin contamination (Figure 1).
Figure 1. Factors influencing the development of necrotic enteritis | Source: BIOMIN
Diet constitutes a key risk factor having a strong impact on the incidence of necrotic enteritis in broiler chickens. Indigestible dietary protein, such as that found in animal proteins like meat and bone meal or fishmeal, cannot be digested and absorbed in the upper part of the intestinal tract. Instead, protein builds up in the lower portion of the intestinal tract, which can then act as a substrate for the gut microbiota. The fermentation of protein produces unfavorable by-products such as amines and ammonia, increasing intestinal pH and encouraging the proliferation of pathogenic bacteria.
One solution to reduce bacterial growth and activity is to limit their access to protein, a key nutrient source. Many producers switch to an all-vegetable diet, for example. Increasing digestibility of nutrients so they are absorbed and utilized by the bird instead of the microbiota is another option. Some phytogenic feed additives are capable of increasing endogenous digestive enzyme activity so the bird is better able to break down and absorb protein and other nutrients making them unavailable to the microbiota (Figure 2). Supplementation of exogenous proteolytic enzymes is another method that can help break down excess protein.
Figure 2. The effect of phytogenic feed additives on apparent ileal digestibility in broiler chickens. (Hafeez et al., 2015)
Microbiota and GIT development
The immediate post-hatch period is a critical time for the development of a chick’s intestinal tract. The changes occurring during this period depend entirely upon appropriate microbial colonization. Application of probiotics in the hatchery and as soon as they reach the broiler house provides an ideal opportunity for beneficial bacteria to colonize the digestive tract before chicks are exposed to potentially pathogenic bacteria and fungi in the broiler house, aiding the development of the digestive tract and helping to protect against enteric infections (Table 1).
Table 1. The effect of probiotics on lesion scores, mortality, and C. perfringens CFU counts in bird experimentally challenged with necrotic enteritis. (McReynolds et al., 2009)
|Lesion Score||Mortality||Log10 CFU/g|
|Negative Control||0.29b||0/50 (0%)||1.00b|
|Positive Control||1.33a||13/50 (26%)||3.42a|
Coccidial infection, resulting either from natural disease outbreak or from introduction at low levels through live coccidiosis vaccination, can damage the intestinal epithelium, allowing the leakage of plasma proteins into the intestinal lumen –a rich nutrient substrate that C. perfringens can exploit for proliferation and toxin production. This can reduce performance and predispose birds to necrotic enteritis.
Probiotics and phytogenic feed additives, with or without the use of coccidiostats or vaccines, can help alleviate the negative effects of coccidial infection. They have been shown to reduce oocyst shedding, severity of intestinal lesions, and adverse effects on performance, demonstrating their status as a promising ‘anticoccidial’ (Figures 3 and 4).
Figure 3. The effect of probiotics with and without coccidia vaccine on intestinal lesion scores during a coccidial challenge. (Ritzi et al., 2016)
Mycotoxins – toxic fungal metabolites produced by common molds found in many components of poultry diets— can directly reduce gut integrity, thus leading to decreased absorption and digestion of dietary nutrients and increased intestinal barrier permeability. Reduced nutrient uptake and leakage of plasma proteins into the lumen due to this breach results in increased protein concentration in the intestinal lumen, providing a substrate for C. perfringens proliferation.
Mycotoxins also adversely affect immunity and have a strong correlation with enteric infections (Table 2). Given the numerous harmful effects of mycotoxins, a proper mycotoxin management program is essential to protect intestinal integrity.
Table 2. The impact of DON on the percentage of birds affected by necrotic enteritis (NE). (Antonissen et al., 2014)
|Group||DON||C. perfringens||% of animals with NE lesions|
|C. perfringens alone||-||+||20 ± 2.6b|
|C. perfringens + DON||+||+||47 ± 3.0a|
|DON alone||+||-||0 ± 0.0|
|Negative Control||-||-||0 ± 0.0|
PoultryStar® is a well-defined, poultry-specific, multi-species synbiotic product that promotes a beneficial gut microflora through the combined action of carefully selected probiotic microorganisms and prebiotic fructooligosaccharides.
Antonissen G, Martel A, Pasmans F, Ducatelle R, Verbrugghe E, Vandenbroucke V, Li S, Haesebrouck F, Van Immerseel F, Croubels S. The Impact of Fusarium Mycotoxins on Human and Animal Host Susceptibility to Infectious Diseases. Toxins. 2014; 6(2):430-452.
Hafeez A., Männer K., Schieder C., Zentek J.; Effect of supplementation of phytogenic feed additives (powdered vs. encapsulated) on performance and nutrient digestibility in broiler chickens, Poultry Science, Volume 95, Issue 3, 1 March 2016, Pages 622–629, https://doi.org/10.3382/ps/pev368
McReynolds J., Waneck C., Byrd J., Genovese K., Duke S., Nisbet D.; Efficacy of multistrain direct-fed microbial and phytogenetic products in reducing necrotic enteritis in commercial broilers, Poultry Science, Volume 88, Issue 10, 1 October 2009, Pages 2075–2080, https://doi.org/10.3382/ps.2009-00106
Reisinger, R., Steiner, T., Nitsch, S., Schatzmayr, G., Applegate, T.J. (2011) Effects of a blend of essential oils on broiler performance and intestinal morphology during vaccine exposure. J. Appl. Poult. Res. 20, 272–283.
Ritzi, M. M., Abdelrahman, W., van-Heerden, K., Mohnl, M., Barrett, N. W., & Dalloul, R. A. (2016). Combination of probiotics and coccidiosis vaccine enhances protection against an Eimeria challenge. Veterinary Research, 47, 111. http://doi.org/10.1186/s13567-016-0397-y