Previously, we discussed the benefit of using a combination of organic acids and probiotics. We will now discuss why using organic acids in combination with just the animal's own indigenous intestinal microbiota may be a different, and perhaps more effective, option.
At birth, an animal’s gastrointestinal (GI) tract is generally considered to be sterile (although evidence is emerging to challenge this). The GI tract is subsequently colonized by microorganisms present in the birthing and immediate neonatal environment. The initial colonizing microbiota may be composed of pathogens, opportunistic pathogens and, of course, beneficial microbes, all of which play a key role in shaping the future composition of the intestinal microbiota.
Intestinal microbiota
The relationship between the host and its intestinal microbiota is complex but critical to its health and prosperity. It is estimated that the body contains 10 times more bacteria than host cells, with the majority of these bacteria residing in the intestine. Given the number and metabolic activity of these cells, it is clear why the intestinal microbiota is now considered by many to be an organ in itself. The intestinal microbiota performs a number of important functions from gut development to oral tolerance (where the immune system is educated to differentiate between, and respond appropriately to, normal and foreign microbes in the intestine). Moreover, the indigenous, intestinal microbiota produces antimicrobial compounds (e.g., organic acids) and, through colonization of mucosal surfaces, provides a barrier (colonization resistance) to (potential) pathogens entering the GI tract. The beneficial functions of the intestinal microbiota are clearly demonstrated by animals raised in environments devoid of microbes (germ-free) who exhibit compromised intestinal development and greater disease susceptibility.
As well as the specific initial colonizing microbes, numerous other factors (e.g., diet composition) will influence the composition of the intestinal microbiota. It is clear, therefore, that this can lead to very significant differences in the exact composition of the gut microbiota between farms and even between individuals on the same farm. This means that the use of feed additives to improve the gut health of animals should ideally seek to work with the existing, relatively stable, indigenous microbiota rather than attempting to drastically change or replace it.
This is where organic acid-based products are particularly useful. Through the differing susceptibilities of individual microbes to organic acids, we can influence the intestinal microbiota in favor of the acid-tolerant, beneficial bacteria at the expense of susceptible, detrimental bacteria. Modifying the existing, indigenous microbial composition in this way, rather than trying to establish foreign (to the species of interest or the particular farm environment) bacterial strains in the gut environment (e.g., probiotic application), will be a more efficient and effective method of improving gut health. To be effective, probiotics appear to require a window of opportunity to colonize the intestine. This may occur after birth, antibiotic use, diet change, intestinal infection, etc., but still requires the probiotic strain(s) to survive intestinal transit and be able to colonize the intestine of the relevant species. These factors underline the value of working with/manipulating the microbes that have already survived the gastric phase and have established themselves in the intestine, which we can do with organic-acid based products.
Organic acid supplementation
Work by Nava et al. (2009), utilizing PCR-based approaches to examine changes in the ileal microbiota of broiler chickens demonstrated that organic acid supplementation increased the numbers of beneficial gut bacteria (e.g., lactobacilli). It was reported that an organic acid blend (including formic and propionic) added to the drinking water resulted in much greater numbers of lactobacilli in the lumen of the ileum than either the control or antibiotic (bacitracin) supplemented group (Figure 1). Although in this study the numbers of lactobacilli were not significantly reduced by the antibiotic compared to the control, antibiotics can have broad antimicrobial activity and, in fact, many specifically target gram-positive bacteria, which would encompass the beneficial bacteria, such as lactobacilli.
The importance of the intestinal microbiota to animal health and performance, and thus producer profitability, cannot be over-stated. Following birth, the apparently sterile intestine is colonized by vast numbers of microbes. This microbial community will consist of those microbes that are indigenous to that particular species and its environment, and have already overcome the inherent hostility of the GI tract. The most effective method of improving gut health would, therefore, seem to be by positively influencing this resident intestinal microbiota in favor of the beneficial bacteria at the expense of the detrimental bacteria.
References
Nava, G.M., Attene-Ramos, M.S., Gaskins, H.R., and Richards, J.D. 2009. Molecular analysis of microbial community structure in the chicken ileum following organic acid supplementation. Veterinary Microbiology 137:345–353.
