Even though there are usually no visible clinical signs, NE still causes tremendous financial losses to the global poultry production industry, estimated to reach $2 billion each year (Timbermont et al., 2011).
The occurrence of mortality due to the outbreak of NE can range from 1% in mild cases up to 50% in which clinical signs such as severe depression, diarrhoea, dehydration, a decrease in feed intake, ruffled feathers or reluctance to exercise can be seen (Lee et al., 2011). The traditional way of treating and preventing NE is by using antibiotics in therapeutic doses via the water and feed.
Lantibiotics instead of antibiotics
Due to the consumers' growing consciousness regarding the use of antibiotics in animal nutrition and the development of multiple pathogen resistance associated with the practice of using antibiotics on a big scale, alternatives need to be found. One of the promising classes of new antibacterial agents are the so called lantibiotics which are antimicrobial peptides produced by Gram-positive bacteria and are encoded on the bacterial genome.
Lantibiotics have a dual mode of action. Firstly, they form pores which induces significant thinning of the outer membrane of harmful bacteria, making them more vulnerable. Secondly, they inhibit cell wall biosynthesis, challenging the target cell in a severe way. Nanomolar levels of lantibiotics can already exert serious negative effects on damaging bacteria. One, which is classified as being a lantibiotic is lichenicidin, produced by a strain of Bacillus licheniformis, was shown to be effective in the inhibition of Clostridium perfringens which is responsible for producing toxins that cause NE (Begley et al., 2009; Draper et al., 2015).
Probiotics can help
In field trials, birds infected with Clostridium perfringens showed an improved body weight gain and lower mortality when fed a diet supplemented with a probiotic containing Bacillus licheniformis producing lichenicidin. In addition, stress factors of all kinds such as heat stress, vaccination or stocking density can increase the prevalence of Clostridium perfringens (Timbermont et al., 2011). This is due to the activation of the vagus nerve, which leads to a decrease in gastric motility and an increase in intestinal motility leading to the alteration of the feed passage rate (Wang et al., 2010). The changes in intestinal microflora impair the gut integrity leading to bacterial overgrowth, creating favourable conditions for the growth of Clostridia spp.
A probiotic can mitigate the effects caused by stress. One mode of action is competitive exclusion, a principle stating that two species with the same niche cannot coexist because one will always outcompete the other. The aim is that the bacterial strain of the probiotic colonizes the gut faster than potentially harmful bacteria, so not giving the opportunity for colonization, preventing dysbacteriosis of the gut microflora (Ibnou-Zekri et al., 2002; Pascual et al., 1999). In addition to the competitive exclusion mechanism, there is also a direct antagonism towards Clostridium perfringens when producing lichenicidin by the probiotic.
Proven effects of B-Act®
Numerous studies show the positive effects of B-Act®, a probiotic feed additive containing viable spores of a strain of Bacillus licheniformis producing lichenicidin on suppressing NE in broilers. One trial carried out using 400 Cobb 500 birds shows the ability of B-Act® to manage NE induced by an oral gavage of 108 CFU/bird of Clostridium perfringens on days 19, 20 and 21 of age. The birds, vaccinated with a coccidiosis vaccine at hatch, were assigned to two different treatment groups. A control group with no added feed additives and a group fed the probiotic feed additive at 1.6*1012 CFU Bacillus licheniformis/mton feed.
A necropsy on 160 birds from each treatment group was carried out on day 22 and NE lesion scores were evaluated. The average NE score was significantly lower in the group fed the probiotics (Table 1). This clearly shows the effectiveness of the probiotic B-Act® in controlling NE outbreaks.
Furthermore, mortality was significantly reduced in the probiotic group. Being able to influence NE in a positive way also resulted in improved average weight and feed conversion ratio. This means that the usage of a probiotic also gives economic benefits for the end user, especially when Clostridium perfringens is prevalent.
Conclusion
Even though NE is not seen as a serious problem in some parts of the world due to the lack of clinical signs, it is still a disease with significant economic effects. The disease can be successfully prevented by using B-Act®, a probiotic containing viable spores of Bacillus licheniformis. This is an alternative to the traditional treatment of NE and might add to strengthening consumer trust in sustainable animal production.
References are available on request
