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Understanding necrotic enteritis
Necrotic enteritis affects poultry flocks around the world. It can occur in an acute form, which makes chickens obviously ill and causes high mortality, but the more common form is subclinical, which might not be as obvious but significantly affects performance and profits.
Necrotic enteritis can be controlled with a combination of management techniques, attention to diet, good control of coccidiosis and with the help of Clostridium perfringens type A toxoid, the first vaccine available for managing necrotic enteritis in poultry.
Following are some facts and figures to help you better understand the disease and its various forms.
Facts about necrotic enteritis
- Necrotic enteritis (NE) is a common intestinal disease of chickens. Over 95% is due to C. perfringens type A, although type C can also cause NE. (See Figure 1).
- NE significantly contributes to poor animal welfare because it causes intestinal disease that makes chickens ill
- C. perfringens is a common inhabitant in chicken intestines and causes intestinal disease only when it grows unchecked, producing a toxin that damages the intestinal lining.
- NE is closely tied to the parasitic disease coccidiosis, which damages the intestines and provides an ideal environment for C. perfringens to take hold and proliferate. That’s why good control of coccidiosis is needed to prevent NE.
- NE used to be well controlled in most commercial birds because they received in-feed antibiotic growth promoters (AGPs) as well as ionophores, a type of antibiotic, for control of coccidiosis. Some of these antibiotics also controlled C. perfringens, but antibiotic resistance has developed. Ionophores also helped control NE by preventing coccidiosis, but coccidial resistance to the drugs has developed; less effective coccidiosis control has contributed to an increase in NE.
- Another reason for the upsurge in NE is the declining use of antibiotics by poultry producers. This trend was initiated by public concern that using certain antibiotics in food animals may contribute to antibiotic-resistant infections in people.
Figure 1. C. perfringens, the cause of necrotic enteritis, is a rod-shaped, anaerobic bacterium.
Clinical (acute) NE
- Clinical or acute NE is usually easy to detect because there is a sudden, high death rate that ranges anywhere from 2% to 50%. In less severely affected flocks breaking with clinical NE, birds may exhibit depression, poor appetite, ruffled feathers and diarrhea.
- With clinical NE, the intestines have a classic “Turkish towel” appearance (Figure 2) upon necropsy. There may be inflammation of the liver (Figure 3).
- Antibiotic-free flocks are at greatest risk for clinical NE. Conventional flocks might also be at risk if bacterial and/or coccidial resistance has developed to in-feed drugs typically administered, such as AGPs or ionophore anticoccidials.
Figure 2. Clinical NE causes a classic “Turkish towel” appearance on the intestinal lining.
Figure 3. Necrotic enteritis can also cause liver damage.
Subclinical NE
- Subclinical NE can be difficult for producers to detect because the only signs of trouble may be a subtle decline in weight gain and feed efficiency.
- The intestinal damage caused by subclinical NE is similar to that caused by clinical NE, but is less severe and may require an experienced eye to detect.
- Careful examination upon necropsy reveals a damaged intestinal lining. The surface is rough and covered with mucus. There may be circular lesions covered with a yellow material (Figure 4). Liver damage might also occur; in a study conducted in Norway, liver condemnations in broilers due to subclinical NE were as high as 20%.
Figure 4. Subclinical necrotic enteritis causes small erosions of the intestinal lining that are circular and covered with yellow material.
- The incidence of subclinical NE is not really known because the disease is so difficult to detect.
- Experts believe that subclinical NE is a greater problem than clinical NE and probably far more costly. The cost of subclinical NE is estimated to be 5 cents per bird or at least $2 billion annually on an worldwide basis.
- Conventional flocks receiving some type of antibiotic are also vulnerable to subclinical NE. For instance, those receiving an AGP as well as an ionophore, an anticoccidial with antibiotic activity, can develop subclinical NE if bacterial resistance has developed to the antibiotics. Subclinical NE can also develop if coccidia become resistant to anticoccidials, resulting in poor coccidiosis control.
Control of necrotic enteritis
- Control of NE requires action on several fronts.
- Good hygiene, proper flock density and correct litter moisture can help.
- Good coccidiosis control is imperative since coccidiosis is linked to the development of NE.
- A low density, high-quality diet fortified with amino acids helps prevent NE. High protein diets should be avoided.
- Vaccination of broiler breeders with Clostridium perfringens type A toxoid,the first clostridium toxoid for use in poultry currently being used in the United States under a conditional license, provides an aid in the control of NE. When broiler breeders receive the NE toxoid, they develop immunity against C. perfringens that is passed on via the egg yolk to progeny broiler chicks (Table 1).
- Field trials have demonstrated that immunization of breeders with the NE toxoid can help prevent NE and improve performance in broiler flocks at risk for NE.
Table 1. Antibody titers determined by hemolysis inhibition assays in egg yolks collected from hens of various ages vaccinated with the NE toxoid are significantly higher compared to controls.
Group | 40 weeks of age | 52 weeks of age | 65 weeks of age |
Vaccinates | 512 | 2,048 | 64 |
Controls | ≤ 2 | 2 | <2 |
