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Broiler intestines with moderate necrotic enteritis lesions.
Necrotic enteritis is a worldwide problem in the broiler industry. The subclinical form of the disease is considered to be more of an economic burden than the clinical form, because of its insidious nature. It has been estimated that annual economic loss due to necrotic enteritis outbreaks amounts to some US$2 billion. Although the disease is primarily caused by bacteria, dietary factors have been identified as one of the most important predisposing factors for necrotic enteritis.
Necrotic enteritis causes
Enteric diseases are of paramount concern to the poultry industry because of production loss, increased mortality, reduced welfare of birds and increased risk of contamination of poultry products for human consumption. Necrotic enteritis is one such enteric infectious disease, caused by Clostrodium perfringens, a ubiquitous, gram-positive, spore-forming, extremely prolific, and toxigenic bacteria that can be found in soil, dust, feces, feed, and used poultry litter.
There are five types of C perfringens (A, B, C, D and E) and necrotic enteritis is caused by toxins produced by C perfringens type A or C. Recently, it was established that alpha toxin is not an essential virulence factor in necrotic enteritis in broiler chickens and only certain strains of C perfringens are capable of producing necrotic enteritis under specific conditions
The disease usually occurs in broiler chickens at 2-6 weeks of age. Necrotic enteritis has been reported in many bird species. Among chickens, the disease is more common in broilers; however outbreaks in layer pullets and adult layer chickens have also been reported. The disease may occur as either an acute or subclinical condition. The subclinical form of the disease has become an economically significant problem for the broiler industry worldwide, as the routine use of antibiotic growth promoters have been banned from poultry feed due to concern over antimicrobial resistance and this has contributed to the higher prevalence of the disease.
Predisposing factors for necrotic enteritis
The key factor for the development of necrotic enteritis is an intestinal environment that favours growth of C perfringens. Feed composition and feeding practices are assumed to affect disease incidence of necrotic enteritis in broilers.
The nature of the diet is an important factor that influences the incidence of necrotic enteritis.
Broiler intestine exhibiting severe necrotic enteritis lesions.
Clinical signs and lesions
The clinical appearance of necrotic enteritis may vary significantly from nothing more than impaired performance to sudden and high mortality. The disease can affects birds of almost any age, but most commonly occurs in broilers of two to six weeks of age. Early sign of necrotic enteritis are often wet litter and diarrhea. Usually there will be depression, ruffled feathers, closed eyes and dark coloured diarrhea in the infected birds. There will be depression in growth rate and feed efficiency, which is generally noticed at a later stage due to damage to the intestine and subsequent reduction in digestion and absorption of food.
The disease pattern may vary, depending on the factors such as immunity and management including types and programme of in-feed additives. Mortality rates may sometimes rise to 50%. Necrotic enteritis can be diagnosed from the typical gross intestinal lesions from post-mortem findings and a gram-stained smear of a mucosal scraping that exhibits large, gram-positive rods.
Necrotic enteritis is a bacterial disease and routine use of antibacterial compounds such as Bacitracin (50 g/ton feed), Lincomycin (2g/ton feed), Virginamycin (20 g/ton feed) in the feed of broilers can prevent the occurrence of necrotic enteritis in broilers. However, legislation prohibits the use of antibiotics as growth promoters in animal feed in key broiler production areas of worldwide.
This has necessitated the industry to evaluate suitable alternate control measures. Diet is an important contributor to necrotic enteritis in broilers, and feeding practices can reduce the disease’s incidence. Among dietary practices that can be followed to reduce the incidence of necrotic enteritis are the following:
Necrotic enteritis is a widespread disease in the broiler industry of significant economic importance. The disease is primarily caused by a bacteria (C perfringens), and can be prevented effectively by antibiotics addition thorough feed.
Feed composition and feeding practices are one of the important predisposing factors for necrotic enteritis in broilers. If proper feeding practices and good management are followed, the incidence of necrotic enteritis can be effectively minimized in broilers in the era of antibiotic-free poultry production.
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