Using antibiotics in agriculture is coming under intense scrutiny and indeed there is a huge drive to reduce it by using alternatives. The emphasis, however must be on prevention to reduce need rather than anticipating a range of alternative therapeutic replacement, one researcher has found.
The focus on the use of antibiotics in agriculture is an area of increasing concern in the specific context of developing antimicrobial resistance (AMR) and the potential catastrophic consequences for human health care. The One Health concept recognises that the health of humans is connected to the health of animals and the environment and it is not appropriate to address the priorities of either in isolation.
The emphasis on agricultural use is perhaps understandable given that across Europe a majority of antibiotics are used in veterinary medicine; specifically in food producing animals. This generic statement masks considerable species specific variation. Nevertheless a reduction in agricultural use as a whole has been identified as a priority, not least in the recently published O’Neill Report (Tackling Drug Resistant Infections Globally) where points 3 and 6 respectively of the summary action plan were ‘reduce unnecessary use in agriculture’ and ‘promote the development of vaccines and alternatives’.
Dr Fiona Roberts, a technical manager with Integra Food Secure Ltd in Oxfordshire, England, specialises in inspecting products back through to the primary end of the food chain, in the areas of food safety and animal welfare. Roberts has carried out extensive research into pigs and poultry and has produced several research papers on various aspects of feeding and treating them. Specifically looking at the use of antibiotics in pigs Roberts explained that historically, the pig sector has been perceived as a ‘high user’ of antibiotics. Elaborating, she said: “This is related to the comparatively intensive production practices and previous widespread use of antibiotics at sub-therapeutic levels as digestive enhancers to promote growth. While this specific practice no longer occurs, the mechanism by which antibiotics create this production ‘uplift’ has been the subject of investigation.
“The role of the intestinal microbiome is key in this respect. It is known that the relative bacterial composition in the gut is crucial to health and welfare but exactly how this in turn mediates growth responses to antibiotic use is still unclear. It has been demonstrated that combined therapies affect population distribution including an increase in proteobacteria and e.coli but a decrease in Bacteroidetes; but perhaps of more concern an associated increase in the prevalence of genes associated with antibiotic resistance. “While a reduction in use (particularly of critically important antibiotics (CIA) such as third and fourth generation cephalosporins and fluoroquinolones) is broadly accepted as a target, the farming community would be wrong to assume that there is much on the horizon in the way of near-market alternatives and certainly in the pig sector the emphasis and direction must be prevention to reduce need rather than anticipating a range of alternative therapeutic replacement.”
On a fundamental level the most basic strategy that all pig producers should apply as an alternative to antibiotic use is ‘Herd Health Planning’ that puts reduction in antibiotic use as the core objective, and not just a hopeful consequence. There is an inevitable focus on the more obvious aspects such as biosecurity and disease prevention through established approaches, for example, vaccination; but thinking more broadly is crucial. Roberts says: “This includes improving animal welfare, given that stress is known to affect both susceptibility to pathogens and to the microbiome, in transport and weaning, both increase the level at which S. enterica is shed faecally. Therefore a management approach that aims to minimise environmental stressors, such as reducing stocking density, mixing, moving, avoiding abrupt dietary transition and competition and optimising enrichment provision, should underpin all antibiotic reduction strategies.
“Simple restriction alone will not solve the problem because once the underlying damage has been done then AMR bacteria will establish a presence in the GI tract and then be disseminated in the environment. The longer term answer to the issue of AMR must address microflora rehabilitation and it is known, for example, that dietary changes have the potential to change the microbiome and cause selective proliferation of organisms.” However, this poses the question of can this be used as a basis for reducing antibiotic requirements and potentially correcting established changes in bacterial populations? For Roberts, the answer appears to be yes and integrated nutritional management is one approach that can both seed and feed favourable organisms in the gut while ‘weeding’ out the unfavourable ones. Approaches/ products that are already available to pig producers include probiotics, enzymes, prebiotics, plant extracts and integrated nutritional management.
“Inevitably, consideration of nutritional inputs means that the whole issue of feed and feeding must be approached rather differently, and already the era of least cost formulation appears to be receding,” said Roberts. “Functional components that actively promote changes within the microbiome have been identified and the dietary inclusion of Mannan Rich Fractions (MRF) is just one approach proving commercially successful. “Most MRF are derived from the cell wall of the yeast Saccharomyces cerevisiae. They are a class of prebiotics that work via pathogen exclusion and microbiome rehabilitation. Commercially available variants have been developed for pigs and poultry. Documented effects include; reduction in total pathogen load, reduction in E.coli, Salmonella and suppressed growth of ESBL e.coli and erythromycin resistant pseudomonas. Additionally and importantly, use of MRF favour preferential growth of high level microfloral diversity and both diversity and complexity correlate well with increased pathogen resistance and pig growth rates.
“Approaches to antibiotic reduction and replacement need to be workable within the context of each individual unit’s production system, but in a global market, producers must also develop awareness of any strategies that may have commercial limitations. While there has also been considerable interest in the inclusion of PAP such as spray dried blood plasma (particularly in piglet feeds) these should be adopted with a note of caution in relation to potential constraints. There is no doubt these products have positive production effects including reduced inflammatory response, improved nutrient utilisation and direct antimicrobial effects, and to a more significant extent than non-PAP alternatives such as potato or egg yolk derivatives. However, use of PAP is still precluded in the UK and as such many retail markets will not accept product from supply chains, even those outside the UK, where these constituents are used.
“Ultimately, while reduction in antibiotic use (particularly CIA) is a valid aim, restricting antibiotics will not remove existing resistance. On farm strategies need to consider several elements including the rehabilitation of the intestinal microbiome; pathogen exclusion (through a co-ordinated plan mapped within VHP that encompasses biosecurity, hygiene and vaccination strategies); the use of nutritional synergy and ultimately a co-ordinated review of prescribing and administration practices. This includes identification of clinical conditions where NSAIDS and analgesics may be the preferable palliative option. “Hopefully, pig production will then have reached a point where the maxim ‘as little as possible, but as much as required’ genuinely applies to pig production in a manner that safeguards both human and animal health,” Roberts concluded.