Bacterial Lameness And The (Non)Sense Of Probiotics

Wouter Van der Veken

A challenge that has recently re-emerged in modern broiler production is the occurrence of bacterial lameness. Recent research indicates that the increased prevalence of bacterial lameness is linked with a general decline in gut health.

An example of such lameness in broilers is femoral head necrosis, whereby bacterial infection delivered via the bloodstream is a prerequisite. Importantly, overt intestinal damage is not required: translocation is linked to general dysbacteriosis which leads to decreased gut integrity including reduced functioning of the tight junctions. These multiprotein junctional complexes act as the seals between the epithelial cells, effectively forming a barrier between the bloodstream and the intestinal lumen. However, when the integrity of the tight junctions is compromised, bacteria in the intestinal lumen can pass between the cells in the gut wall and end up in the bloodstream on the other side of the gut wall. This facilitates the transportation of bacteria from the gut to different organs and parts of the animal, where they can then cause infections in locations they would otherwise never be able to reach.

One prime location for infection is the cartilage of rapidly developing bones, especially in bones that are under high physical stress. Infections happen much more easily in such cartilage due to microfractures, also known as osteochondrotic clefts, that result from rapid development combined with high stress forces. An example of such a location is the femoral head of the lower limbs.

Over the last few years, Enterococcus spp. have been identified as one of the most prominent translocators and causative agents of bacterial lameness. The translocation and subsequent infection often take place in the first week of life, but the bacteria remain present in the intestines for multiple weeks. To combat the challenge, multiple factors need to be considered: hygiene management, feed formulation and even house layout can all play a role. Focusing on the feed side, feed additive application is considered for two reasons:

  • to combat Enterococcus specifically
  • to reduce the risk of the bacterial translocation by securing general gut health

Although it might make sense to focus on Enterococcus specifically, there are some considerations to keep in mind. First, most of the research where specific feed additives have been tested against Enterococcus were conducted in vitro. Despite the wide range of test methods, in vitro can never fully mimic an in vivo situation and so does not always offer a clear picture of true product efficacy in the field.

Second, targeting Enterococcus specifically has its downsides: there is not one Enterococcus strain identified as being solely responsible for all bacterial lameness. Enterococcus as a bacterial genus is not only pathogenic, but it also compromises multiple lactic acid bacteria which are part of a normal, commensal and well-functioning microbiota. Adding feed additives focused on reducing Enterococcus is thus not advisable, while feed additives that only reduce specific Enterococcus strains will not be able to cover all the potentially pathogenic strains.

Finally, bacterial lameness can also be caused by other bacteria besides Enterococcus. As such, there is little sense in focusing only on this bacterial genus when aiming to combat the challenge of bacterial lameness.

Alternatively, feed additives that protect and support general gut health make more sense. Not only do they guard and improve gut function, but their non-selective action regarding the integrity of tight junctions means that they will aid in reducing translocation altogether, regardless of the bacterial type trying to do so. Yes, Enterococcus is a major player in bacterial lameness, but not the only one!

In addition, bacterial lameness is not the only resulting issue of bacterial translocation. It is thus important to minimise all bacterial translocation, not only that of Enterococcus. Considering that translocation is just one of the possible outcomes of dysbacteriosis, technical performance itself will also be affected, as gut function decreases when dysbacteriosis occurs. Taken together, these arguments make it clear that reducing dysbacteriosis makes the most sense when supporting efficient animal production.

An example of a feed additive focusing on general gut health is B-Act®. It contains a unique probiotic Bacillus licheniformis strain, selected specifically to aid in the prevention and mitigation of dysbacteriosis, thereby reducing the risk of lameness in the process. To test the theory, an in vivo trial was set up to evaluate the effect of B-Act® in a bacterial lameness trial model. A total of 120 Ross 308 broilers were divided into three treatment groups and housed in pens with an uneven surface (wire floor). The latter condition was added to increase stress on the cartilage of joints and bones, aiming for a higher chance of osteochondrotic clefts and thus an increased number of infection sites. Simultaneously, all animals received a challenging diet (more fibrous, less digestible) aimed at inducing dysbacteriosis and subsequent bacterial translocation. The difference between the treatment groups was that they either received B-Act® from start to finish (1.6 x 1012 CFU/ton of feed), a treatment dose of enrofloxacin from day 38 to day 47 (10 mg enrofloxacin/kg body weight) or nothing at all (control group). The trial lasted 53 days.

Figure 1 shows the final percentage of lameness for each group, indicating that the model to induce bacterial lameness was successful. 

 

Figure 1. Lameness percentages on day 53 in all three treatment groups. Different superscripts indicate significant differences at p < 0.05

 

Both the antibiotic treatment and B-Act® mitigated the level of lameness significantly (p < 0.05). The onset of the first cases of lameness were 5 to 6 days later in the treatment groups compared to the control group. 

Keeping the above in mind, bacterial lameness is firmly rooted in general gut health. Managing dysbacteriosis is thus essential in the prevention and mitigation of bacterial lameness. To do so, multiple factors play a role, including feed additives such as probiotics. Within this group, those probiotics focusing on general gut integrity make the most sense. B-Act® is a prime example of a probiotic with proven efficacy going above and beyond its impact on technical performance.