The issue of antimicrobial resistance is of global concern across human and animal health. In 2016, the UK government committed to new targets for reducing antimicrobial use (AMU) in livestock. Although a number of metrics for quantifying AMU are defined in the literature, all give slightly different interpretations. This paper evaluates a selection of metrics for AMU in the dairy industry: total mg, total mg/kg, daily dose and daily course metrics. Although the focus is on their application to the dairy industry, the metrics and issues discussed are relevant across livestock sectors. In order to be used widely, a metric should be understandable and relevant to the veterinarians and farmers who are prescribing and using antimicrobials. This means that clear methods, assumptions (and possible biases), standardised values and exceptions should be published for all metrics. Particularly relevant are assumptions around the number and weight of cattle at risk of treatment and definitions of dose rates and course lengths; incorrect assumptions can mean metrics over-represent or under-represent AMU. The authors recommend that the UK dairy industry work towards the UK-specific metrics using the UK-specific medicine dose and course regimens as well as cattle weights in order to monitor trends nationally.

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Due to scientific, public and political concern regarding antimicrobial resistance (AMR), several EU countries have already taken steps to reduce antimicrobial (AM) usage in production animal medicine, particularly that of the highest priority critically important AMs (HP-CIAs). While veterinarians are aware of issues surrounding AMR, potential barriers to change such as concerns of reduced animal health, welfare or production may inhibit progress towards more responsible AM prescribing. Farmers from seven dairy farms in South West England engaged in changing AM use through an active process of education and herd health planning meetings. Prescribing data were collected from veterinary sales records; production and health data were accessed via milk recording and farm-recorded data. This study demonstrates that cattle health and welfare-as measured by production parameters, fertility, udder health and mobility data and culling rates-can be maintained and even improved alongside a complete cessation in the use of HP-CIAs as well as an overall reduction of AM use on dairy farms. This study also identified a need to consider different metrics when analysing AM use data, including dose-based metrics as well as those of total quantities to allow better representation of the direction and magnitude of changes in AM use.

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Slowing the development of antimicrobial resistance (AMR) requires reducing antimicrobial use (AMU), which necessitates altering prescribing practices and reducing use in food-producing species ( O'Neill, 2015 ; World Health Organisation, 2018 ). The literature has suggested for many years that we should try a different approach to changing practices on farm ( Chambers et al, 1985 ) and calls for more farmer-led initiatives compared with traditional, passive knowledge transfer that commonly occurs in the veterinary profession ( Escobar et al, 2013 ; Kristensen and Jakobsen, 2011 ; Vaarst et al, 2017 ). When it comes to complex issues such as reducing AMU, a farmer-led approach is well positioned to help farmers and veterinary surgeons change their practices. We propose a farmer-led approach has a key role to play in changing behaviour and helping to solve complex challenges such as AMR.