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Growth Hacking: What Studying AGPs Can Teach Us About How to Promote Growth

Understanding how antibiotic growth promoters work provides pathways to boost performance while reducing reliance on antimicrobials and preserving their medicinal value. The latest research investigates the mode of action of antibiotic growth promoters (AGPs) and shows how they can be replaced by novel feed additives.


Antonia Tacconi

Novel feed additives and preventive management strategies can reduce the need for antibiotic use as growth promoters, but it is important to consider more than just one aspect related to the mode of action of AGPs.

The discovery of antibiotics in 1920s revolutionized medicine and saved countless lives. The revelation of antibiotics’ ability to promote growth in livestock at subtherapeutic doses in the late 1940s transformed the animal protein industry, improving profits and enabling us to feed a burgeoning world.

However, the overuse of antibiotics both in humans and in animals has been linked to the higher occurrence of antibiotic resistances in bacteria that jeopardize the efficacy of antimicrobial treatment.

Combating antimicrobial resistance

The United States announced the AMR Challenge: a global initiative to combat the growing threat of antibiotic resistance at the United Nations General Assembly in 2018. The OIE, WHO, and governmental bodies in many countries throughout the world have all taken steps to further study and raise awareness regarding the threat that antimicrobial resistance poses. It is critical that we are able to rely on the efficacy of antibiotics in the future. (BIOMIN has committed to the AMR Challenge to combat antimicrobial resistance.)  

The AMR Challenge calls on governments, companies and NGOs worldwide to make formal commitments that further the progress against antimicrobial resistance. | Source: U.S. Centers for Disease Control

Removing antibiotics from diets

Concerns have been raised in the last decades that subtherapeutic use of antibiotics hastens the  spread of antibiotic resistant bacteria. Mixed opinions still exist whether the use of AGPs really plays a role in the transfer of resistance from animal pathogens to human pathogens. What is clear, however, is that these concerns have led more and more consumers as well as regulatory authorities to push to curtail AGP use, steering the industry towards antibiotic-free feeding.

How antibiotic resistance happens | Source: CDC.gov

Risk of AGPs and antimicrobial resistance

The dosages applied when antibiotics are used as AGPs are lower than the minimum inhibitory concentration (MIC), which is the level needed to make sure that the bacterial growth is inhibited (known as bacteriostatic effect). This indicates that the dosage is too low to be able to suppress the growth of pathogens in the gut, and has also been confirmed by numerous scientific studies.

 

Gut health and performance

Nevertheless, the use of AGPs has been proven to have effects related to the shift of the microbial community in the gut and very often bacteria involved in these shifts are lactobacilli, which are also considered to have both positive as well as negative effects on performance.

Clearly, the gut microbiota plays a very important role by ensuring a good performance, but still more research is needed in order to better understand how an optimal animal gut microbiota should look. For this reason it remains difficult to choose alternatives to AGPs in relation to their effect on the microbial population in the gastrointestinal tract.

Research on AGP modes of action

There are other proposed modes of action of AGPs seeming to be important for a good animal performance. These proposed mechanisms could be addressed with alternative products available on the market.

Table 1. Proposed modes of action of AGPs

MechanismReference
Anti-inflammatory effectNiewold, 2007
Promotion of a balanced gut microbiotaGaskins et al., 2002; Costa et al., 2017
Improved fat digestiblity and energy uptakeLin, 2014
Quorum quenchingBroom, 2017
Reduction of bacterial growthReeks et al., 2005

Source: BIOMIN

Examples for the modes of action that could be targeted are: (i) the anti-inflammatory exerted by antibiotics, (ii) the promoted balance of the microbiota, (iii) a better digestibility of fat and energy uptake, (iv) the quorum quenching or inhibition of cell-to-cell communication effect of antibiotics at sub-lethal dosage), and (v) the capacity of antibiotics to slow-down the growth rate of some bacterial also at dosages below MICs.

Food animals are subject to many factors that can lead to inflammation, which results in ‘wasted’ energy that could otherwise be put towards performance. Plant-based substances with anti-inflammatory effects can limit energy wastage, thereby promoting growth.

Probiotics can both help establishing a healthy microbial environment in the gut and have beneficial immunomodulatory properties.

Digestibility enhancement makes more of the nutritional value of the feed available to the animal. It is also a top reason that livestock producers use phytogenic feed additives.

Bacterial species are now known to coordinate behavior at a multicellular level, known as quorum sensing. Cells produce small, diffusible signal molecules continuously and as the population grows, these molecules accumulate. When molecules reach a certain threshold, concentration changes in gene expression are triggered and lead to changes in population behavior e.g. virulence. The inhibition of communication, called quorum quenching, is possible using quorum-sensing inhibitors found in nature.

It has been demonstrated that organic acids have a direct antimicrobial activity against pathogens such as E. coli and Salmonella, and they might contribute to gut health indirectly by improving digestibility.

When looking for alternatives to antibiotic growth promoters it is important to consider more than just one aspect related to the mode of action of AGPs.

Nevertheless, it is important to recognize that it is not simply a matter of substitution or 1:1 replacement of AGPs with novel feed additives that promote gut health and performance. A holistic approach should be implemented considering nutritional, hygienic and environmental intervention always linked to a robust biosecurity strategy. Increased adoption of novel additives and preventive strategies can reduce the need for antibiotic use as growth promoters of for treatment and to combat antibiotic resistance.

This article originally appeared in Feed Strategy. References available upon request.