Over the last two decades, several types of gut health supporting additives have been shown to have at least the potential to improve gut health and animal performance and as such, to be applied as alternatives to antibiotics. Initial research on these products was largely focused on their direct ‘antimicrobial’ effect, as it was tempting to hypothesize that any successful alternative for antibiotics would need to have a similar (antimicrobial) effect. However, it becomes clearer that gut health additives have working mechanisms that are very different from those of antimicrobials. I will argue that direct antibacterial effects most likely do not underlie the main working mechanisms of additives, and that improvement of the development and application of these additives will depend on the investigation of their mode of action at the microbial and cell-biological level. This will be exemplified with recent research data on different classes of feed supplements, including butyrates, probiotics and phytogenics. Butyrate, for instance, is a molecule that is well known for its ability to elicit numerous effects in the digestive tract. While most publication describe positive effects of butyrate supplementation, I will present data demonstrating that the effects of supplementing livestock animals with commercial butyrate products are heavily dependent on the enteric location where butyrate is delivered in the digestive tract. For example, in at least some conditions, elevated butyrate concentrations in the fore- and midgut of broilers may induce negative effects on caecal microbiota diversity and/or inflammation, as opposed to increased butyrate concentrations in the hindgut. In addition, monoglycerides of short-chain fatty acids, the metabolites of probiotics and the phytochemicals in botanical products are unlikely to have substantial specific bacteriostatic effects, as exemplified by EU-funded study evaluating their effectiveness against Campylobacter. More likely, they exert their function by modulating effects that can be trigger at low intestinal concentration, such as the inhibition of bacterial quorum sensing. Lastly, results will be shown from a trials demonstrating that further improvement in gut health and economic profitability of the producer can be achieved, by implementing research based programs, combining different classes of additives.
Keywords: butyrate, phytogenics, probiotics, working mechanism.