Understanding the role of host-pathogen interactions and the impact of management system on antimicrobial resistance in Brazilian livestock systems

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The Brazilian beef industry is immense, and is a vital source of foreign revenue for the country. Brazil is the second largest producer of beef in the world, and has the world's largest commercial herd of approximately 200 million head produced on 1.8 million farms ranging from small enterprises (<500 head p.a.) to commercialised beef production enterprises (>4000 head p.a.). Most animals are produced on pasture, many of them on soils of low to medium fertility in the cerrado (similar to savannas, an important biome in Brazil) with <7% of slaughtered animals being produced on feedlots. Despite this extensive system of beef production, antimicrobial consumption is high. In 2010, Brazil was ranked third highest in the world for antimicrobial consumption by food producing animals, and accounted for 9% of total global farm animal antimicrobial consumption. This high consumption of antimicrobials by farm animals increases the risk of the development of antimicrobial resistant (AMR) bacteria in the host animal's microbiome (the microbial population living in the animal's gut). There are many factors which might encourage the proliferation of AMR bacteria in the host gut, and the hypothesis on which this proposal is based is that changes in the host microbiome may affect the maintenance and prevalence of AMR strains of bacteria. Identifying interventions that may then encourage the development of a microbiome that suppresses AMR bacteria could then help control the development and spread of AMR in Brazilian beef cattle. We hypothesise that beef finished on pasture in Brazil will have a lower prevalence of faecal AMR bacteria compared with those finished in feedlots, because of the less intensive nature of the pasture based production system. Much of the pasture grazed in Brazil is suitable either for the growth of tropical grasses or, in more intensively managed pastures, legumes. Both tropical grasses and forage legumes contain tannins, which are known to have antimicrobial properties and antibiotic resistance modifying properties. However, the efficacy and mode of action of tannins as antimicrobials depends on their concentration and composition. Elucidating the relationship between tannin composition and intake, and the effect this has on the host animal's microbiome (and susceptibility to AMR bacteria) will be investigated in this project. In the first stage of the project, we will conduct a survey to determine the effect of animal age (yearling and finishing animal) and production system (cerrado grazing, more intensively managed pasture, feedlot) on the prevalence of AMR bacteria in faecal samples taken from beef cattle in Brazil. We will also determine the composition of the microbial population in the animal's gut (from the faecal sample) to investigate whether there are patterns of bacterial species which are associated with a lower prevalence of AMR bacteria. We will also take samples of the forages consumed by the animal and investigate whether the amount and composition of tannin that the animal consumes can explain differences in its gut microbiome and the prevalence of AMR bacteria. This will then enable us to develop management and feeding strategies (that would be investigated in the second stage of the project) that might reduce the prevalence of AMR bacteria in Brazilian beef cattle, improving the health status of the cattle themselves and improving the safety and marketability of the meat.