Does the potential for AMR selection differ between common UK cattle grazing systems?

Antimicrobial resistance (AMR) occurs because repeated exposure to antimicrobial drugs kills susceptible bacteria leaving the resistant types to multiply. Recent high-profile reports of the devastating consequences for human health caused by the resistance of disease-causing bacteria to antibiotics have emphasized the need to understand the processes that drive increasing prevalence of antimicrobial resistance in human and animal pathogens.

Farm animals are considered to be a major source of AMR because of the large amounts of antibiotics used both to treat infection (therapeutic use) and to prevent infection (prophylactic use). However, little is known about the background levels of resistance in farming systems, even when animals are only treated with antibiotics when they need them (therapeutically). For instance, the sharing of genetic material by bacteria that are in close proximity is another route where AMR may emerge unexpectedly in otherwise non-related bacteria. AMR transmission between cattle is likely to be greater when they are close together, for example during the winter housed period. In this proposal we will use an experimental farm where cattle being raised for beef production only receive minimal antibiotic treatment described as 'best practice' by vets. We will monitor dynamics of AMR bacteria and genes in cattle dung in summer when the cattle are grazing in the field, and in the winter when they are housed together. We will carefully monitor cattle who have been sick and have been given antibiotics and those in the rest of the herd.

The diet of farm animals may also effect increased AMR in their gut flora. Even common plants ('forage') like grass and clover that cattle commonly eat when they are out grazing produce natural antimicrobial compounds that may continue to be active in the stomach (rumen) where millions of bacteria thrive and multiply. In the winter, cattle are brought indoors and fed silage which is grassland plants that have been fermented to conserve them. Undigested diet and lots of bacteria from the rumen, and therefore perhaps AMR, are excreted in cow dung. We will analyse the dung of cattle that eat different forage types to find out if what they eat affects the likelihood of AMR arising in cattle fed one diet compared to another.

Most cattle farming in the UK is situated in the hilly 'wet West' where the potential for rain to runoff fields into waterways is high. Recent increases in storms that cause lots of runoff and flooding may be due to climate change, are predicted to continue. At the same time, in recent years there has been an increasing recognition that AMR may arise in farm animals and be released from the farm environment to the natural environment in water and might therefore end up in drinking water, bathing water or in seafood. Normally, pollution from cattle dung in water is monitored using faecal indicator organisms (FIOs), which are bacteria that do not usually cause disease but which correlate with those that do (pathogens), and can be handled safely by scientists. It would be useful to know what proportion of FIOs carry AMR, because they are routinely tested for, facilitating estimates of AMR transmission to be estimated in the future. We will sample water flowing from fields that have been grazed by beef cattle or spread with their manure, and analyse the bacteria in the water including the FIOs to see if they are resistant to antibiotics.

The results of this study should help us to understand whether AMR that arises in cattle herds may be transferred to the environment, whether management can limit AMR and its transport, and inform approaches for assessing risks of new antibiotics and managing adverse effects that might be occurring. It is important work for addressing risk in our complex agro-food system that is clearly important for both consumers and farmers.

The emergence of disease-causing bacteria that are resistant to antimicrobial compounds (typically antibiotics) threatens the global human population. Practicing medics and vets who rely on antibiotics to treat disease in humans and animals will benefit from the new evidence that this project will provide on the baseline levels of AMR in common farming systems in the UK to inform their selection of therapeutic drugs.

This research will determine the levels of abundance and the potential transport of antimicrobial resistance (AMR) from food animals (beef cattle) into waterways in grasslands used for livestock production, so will inform all agencies concerned with risk management in farming systems, including Defra and ADAS.

Grasslands cover 65% of all available agricultural land, and are concentrated in the 'wet West' often on sloping ground with heavy, easily waterlogged soils. Therefore, the trend for increased and intense pulses of rainfall in the region due climate change also raises the potential for movement of waterborne disease-causing bacteria and AMR from dung from grazing animals and manures into waterways and the potential contamination of drinking water supplies. By investigating the effect of management alternatives for forage production at the farm-scale, this project will also provide evidence of how hydrology may be changed and influence the movement of waterborne disease-causing bacteria (indicated by faecal indicator organisms, FIOs) and AMR, of benefit to water companies and the Environment Agency.

Livestock farmers are being blamed for contributing to AMR in the clinic through the overuse of antibiotics, particularly when used prophylactically to prevent rather than treat disease, but drugs are expensive so strategies for reducing disease overall are preferred. Best practice, reactive use of antibiotics is common in British beef farming, so the selection for drug resistance should be much less compared to dairy farming, for example. However, other types of non-drug related antibiotic resistance may arise in beef cattle systems, because forage naturally contains anti-microbial compounds (e.g. phenols) which may cause selection of AMR in the rumen which is excreted in dung into the environment. The close proximity of housed animals may also increases the likelihood of dissemination of AMR bacteria between animals in the same herd in the winter, this will be studied during a summer pasture, winter housed management cycle. This project will determine whether different management of forages affect the potential for AMR to emerge in beef cattle herds, and whether the transfer of disease-causing bacteria and AMR in cattle can be reduced by altering diet.