Microbiota-host interactions. How can dietary strategies help?

Introduction

Food production animals, have been genetically selected towards improved parameters like: feed intake, muscle development, and  milk or egg production. In addition, these animals are reared in conditions that tend to favor pathogen dissemination. High feed uptake rates and quick growth make these animals prone to intestinal disorders, which in the past was disguised up to a certain extent with the use of antimicrobial growth promoters (AGPs).

These compounds were widely used around the globe to maintain profitability in the broiler and pig industries.The inclusion of antimicrobials at sub-therapeutic levels as feed additives, led to increased animal performance. However, such practices also contributed to an increased onset of antimicrobial resistance (AMR), posing very serious health risks for people and animals.

AGP bans: Discoveries behind a very important measure

A ban on the use of AGPs, mainly driven by consumer concerns regarding increases in antimicrobial resistance, was installed in the EU in 2006. This became a global trend and concerns led to use reductions or bans depending on the region. In 2012 the Center for Veterinary Medicine of the US Food and Drug Administration published a ‘Guide for the Industry’ where they stated that antibiotic use must be reserved for disease treatment in specific situations, and not for growth promoting purposes.

The mode of action of AGPs is still a matter of discussion, but a variety of mechanisms have been suggested, including: total bacterial count reduction in the gut (and consequently less competition for nutrients), a reduction of specific pathogens (e.g. Clostridium perfringens), a decreased abundance of specific harmful bacterial properties (e.g. bile salt hydrolase activity and thus poor fat digestion), a reduction of inflammatory reactions associated with a decreased pathogen load, amongst others (Butaye et al., 2003; Knarreborg et al., 2004). Direct immune-modulatory effects associated to AGPs have also been suggested.

Regardless of what the action mechanism of AGPS is, it is evident that host-microbiota interactions are involved. Gut-microbiota interactions are very complex since the gut is an organ that contains multiple cell types that carry out multiple functions. While also serving as a host to a diverse microbiota which also carry out many functions, including the breakdown of dietary molecules and the subsequent production of absorbable products. As well influencing and modifying the maturation and development of the (mucosal) immune system.

Unlocking the potential of the gut microbiome

The term ‘gut ecosystem’ describes the fact that microbiota is part of a single organ, with specific functions. Such functions derive from both the genetic potential of gut microbiota (microbiome), and the functions of the host gut wall. The recent application of novel technologies (-omics technologies) has allowed to obtain a better understanding of host-microbiota interactions. Various studies using 16S rDNA sequencing, specifically led to the identification of microbial taxa associated with beneficial or harmful host responses. Meanwhile the use of metabolomics has allowed the identification of the microbial metabolites that trigger such effects. The production of microbial metabolites can be influenced through the use of nutritional factors. This presents an unprecedented opportunity to make animals more robust and resilient against non-infectious and infectious challenges. Which can potentially result in significant health and productive benefits.