Despite good management practices necrotic enteritis is still a major cause of mortality in broiler growing. Research in Spain proved that adding probiotics to the diet will help in raising healthy birds and minimising the loss caused by this disease.
By Dr Marisol Castillo, Rubinum SA, Spain
Enteric diseases are an important concern to the poultry industry because of poor performance, increased mortality and reduced welfare of birds. In the last decades, antibiotics have been routinely supplemented to poultry feeds in order to control pathogenic and non-pathogenic enteric microorganisms and therefore, to improve growth performance. However, the ban of antibiotic growth promoters (AGPs) in the EU has ended in a more complicated control of particularly enteric avian diseases.
In this regard, and in spite of all the advances in poultry production, there is still one disease that regularly affects chicken flocks, resulting in growth depression around the third week of age, and that is necrotic enteritis (NE).
Recent studies have demonstrated more than 80% of positivity all around the world, with Europe being the region with the highest incidence (94% compared to 89% in USA, 75% in South America and 65% in Asia). Clostridium perfringens type A, producing an alpha toxin is the main bacterium responsible, being associated with a subclinical infection most of the times. Gut mucosa is damaged and digestion and absorption of nutrients is diminished resulting in poorer feed conversion. It leads the feed conversion rate (FCR) to increase around 6-9 points and final body weight to reduce between 3-5%.
Mechanisms largely unknown The mechanisms of colonisation of the avian small intestine and the factors involved in toxin production are still largely unknown. It is well known that the presence of C. perfringens in the intestinal tract of broiler chickens does not lead per se to the development of necrotic enteritis.
Caecum of a broiler bird at necropsy.
Severely damaged caecum of a broiler, caused by Clostridium perfringens.
C. perfringens is taken up from the environment; environmental sources are contaminated feed, water or any part of the broiler production and the environment but it is generally accepted that the combination of several factors is required to produce the disease: feed composition (diets with high levels of indigestible water non soluble non-starch polysaccharides, and high amounts of protein), intestinal damage produced by coccidial pathogens (the leaking of plasma to the intestinal lumen can provide a necessary growth substrate for the bacteria) as well as any other inflammation of the gastrointestinal tract.
Since the EU ban of AGPs, an increase on the incidence of NE has been observed. Therefore, new strategies in the prevention and control of NE are necessary to reduce the incidence of the disease in the poultry industry. Vaccination against C. perfringens, the control of coccidiosis, competitive exclusion products, prebiotics and probiotics can be considered in this way.
Potential tool As is well known, probiotics lead to an optimised gut flora balance, having a direct effect of reducing some gram positive bacteria such as Clostridia. Therefore they should be considered as a potential tool to prevent this disease in poultry. Lactobacilli have demonstrated a reduction of adhesion of C. perfringens in vitro, related with a decrease in mortality due to NE. In a similar way, B. subtilis challenged chickens also demonstrate lower persistence of the bacteria and B. cereus var. toyoi have also demonstrated good effect against Clostridia in swine and rabbits, and also in chicken by a trial run in the Cresa research facilities in Spain recently.
A total of 600 one-day-old male broiler chickens were included in the study. Animals were distributed in 12 groups, with 50 chickens per group. At 7 days of age, chickens were orally inoculated with a mixed inoculum of Eimeria acervulina and Eimeria necatrix. At day 14, 7 days after the Eimeria inoculation, birds were challenged with type A Clostridia perfringens isolate (108 CFU/g feed during three consecutive days (14, 15 and 16 day)). Chickens were examined daily for the presence of clinical signs and the average weight for each pen were obtained weekly.
At days 21 and 28 of age (7 and 14 days post infection), 10 birds of each pen were euthanised and a post-mortem macroscopic examination was performed, and lesions in the duodenum and ileum were scored for each bird. Ileal digesta of each bird was obtained to count Clostridium perfringens by real-time PCR.
Animals with apathy were reduced from 7% in the control positive group to 3% in the probiotic group, a fact that was related with a lower number of animals with injuries compatible with EN at day 28 (10% in control group versus 8% in probiotic group) and lower counts of C. perfringens in the gut (Figure 1).
Reducing clostridia counts So, taking into account these results, and despite lacking performance results (still being analysed), we can conclude that B. toyoi can help in reducing clostridiosis in chickens. B. toyoi is a sporulated gram positive bacteria that directly stimulates lactobacilli and bifidobacteria in the animal gut which could be responsible for reducing Clostridia counts by the production of some specific bacteriocins. Moreover, the increase of the non-specific immune response (higher mucine layer) and gut function and structure may be behind the effects found.
From these results, it can be concluded that a combination of measures that include avoiding predisposing factors and combating the pathogen itself, should be the choice strategy in avian production. Probiotics can be considered in this strategy as effective additives reducing C. perfringens.