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Monitoring and benchmarking AM use – establishing the metrics

Standard measurements used to assess antimicrobial usage in veterinary medicine.
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Monitoring antimicrobial usage levels is essential, not only to ensure judicious use of antimicrobials, but also to facilitate benchmarking of antimicrobial usage levels across multiple farms or practices, to allow the identification of farms with high usage and incentivize reductions in inappropriate usage. There are many methods available to monitor antimicrobial usage, although most commonly used are European standard methodologies, which are designed to allow international comparison of AMU across multiple species. The first main methodology is mass based, with the European standard metric being milligrams of antibiotic used per PCU, population correction unit, which is an estimate of the kilograms of livestock on the farm at time of treatment.
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Secondly, there are dose based methodologies, which include defined daily doses, the number of antibiotic doses an average animal receives in a year, defined course doses, the number of antibiotic courses an average animal receives in a year, and also a myriad of country specific metrics that are not often comparable between one another.
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Mg per PCU is a commonly used European standard metric for calculating the milligrams of antibiotic used per PCU, population correction units, an estimate of the kilograms of livestock present on the farm at the time of treatment. To calculate this metric, the number of milligrams of injectable treatments are calculated and divided by the estimated PCU on the farm. Milligrams of any tube products, such as the lactating cow mastitis tubes, are also divided by the estimated PCU, similarly with any dry cow antibiotic treatments and any off licence treatments being approached in a similar manner. One point of caution to note in the use of this metric is that some antimicrobials have relatively low milligram contents, particularly the highest priority critically important antimicrobials.
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And the preferential use of these products on farms might result in a lower overall mg per PCU figure, regardless of whether they might be considered as inappropriate in many cases. To calculate the PCU, there are standard weights assigned to different groups of animal within various species. And the VMD have provided a summary document explaining the mg per PCU calculation in much more detail.
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Defined daily doses is another standard European metric that aims to estimate the number of doses an animal might receive. The milligrams of injectable treatments are used to estimate how many doses were administered. Individual treatments, such as lactating cow tubes, are now treated as a single unit, rather than their milligrams. And the number of tubes used would be divided by the number of animals present on the farm, rather than their PCU. Longer acting therapies, such as dry cow therapy, were excluded from the calculation of DDD, and similarly, any off licence treatments are also not included.
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Defined course doses are relatively similar to defined daily doses, however, calculates the number of standard courses of an antibiotic an animal might receive. Much of this metric is calculated in a similar manner to define daily doses. However, longer acting tube therapies, such as dry cow tubes are included, although off licence treatments are still not included within this metric.
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With a basic understanding of what these metrics are trying to achieve, it is essential to monitor antimicrobial usage and benchmark against similar systems. The University of Nottingham Antimicrobial Usage Calculator is freely available for both dairy cattle and sheep and allows vets and farmers to input the antimicrobial products used on a farm and calculate the antimicrobial usage by a variety of standard metrics. To complement this tool, there is also a benchmarking tool available. And once antimicrobial usage has been calculated for multiple farms, the benchmarking tool can be used to pull data in from several farms and compare usage levels, allowing easy identification of higher usage levels. The University of Nottingham Antimicrobial Usage Calculator is freely available on the AHDB website.
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There are many methods of monitoring, and benchmarking AMU. The following example uses the freely available University of Nottingham Antimicrobial Usage Calculator and 100 cow dairy farm to illustrate the potential methods of monitoring and benchmarking antimicrobial usage. Firstly, enter the population of animals on a farm. With dairy cattle, this is simply the number of adult dairy cows present on the farm. Secondly, enter the antimicrobial products used within the last year. Thirdly, the tool will analyse antimicrobial usage by mg per PCU, DDD, and DCD metrics and will split the analysis into various treatment routes. Lastly, the freely available benchmarking tool can be used to pull together data from multiple farms and benchmark AMU to identify farms with higher usage levels.
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Once antimicrobial monitoring and benchmarking has taken place, it is important to identify farms with higher levels of antimicrobial usage and determine whether this level might be reduced. From a welfare perspective, it is essential that animals which require treatment receive the appropriate antimicrobials when needed. However, farms with higher levels of AMU either suggest higher disease levels than necessary or treatment practices that involve a potentially inappropriate treatment approach. With farmers, veterinarians, and consultants working together, it should be possible to reduce AMU on farms by reducing both disease levels and inappropriate treatment approaches to dramatically reduce overall AMU. The following example continues using 100 cow dairy herd with a relatively high level of antimicrobial usage.
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By using selective treatment approaches, such as selective dry cow therapy, and reducing mastitis levels, it should be possible to reduce both injectable and tube antimicrobial usage levels. By improving foot health and stopping inappropriate lameness treatments, significant reductions in lameness related AMU should also be achieved. Similarly, by improving calf management and calf health and reducing transition diseases, significant reductions might be achieved in both overall AMU, but also in highest priority, critically important antimicrobial usage levels.
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For further information on monitoring antimicrobial usage, search for the VMD VARRS reports, and for the freely available calculator tools, please visit the AHDB website.

This video describes the standard measurements used to assess antimicrobial usage across farms, and why we would need to be able to make comparisons between different farms and against a benchmark.

The overall idea behind setting a benchmark level of antimicrobial usage in farms is to provide incentives for being below the level, and to identify farms with higher levels of usage so that ways of reducing this can be introduced.

The 2 main categories of monitoring are mass-based and dose-based.

The mass-based measurement is milligrams of antibiotic used per PCU (mg/PCU). PCU is an estimate of the total kg of livestock on a farm at the time of treatment. To gain a better understanding of this measure, please read the guide in the see also section from the VMD.

The 2 dose-based measurements are defined daily doses (DDDvet) and defined course doses (DCDvet). DDDvet is the number of antimicrobial doses an average animal receives in a year; this measurement does not include longer lasting therapies or off-licenced treatments. DCDvet is the number of antimicrobial courses an average animal receives in a year; similarly to DDDvet, it excludes off-licenced treatments, however it does include longer lasting therapies.

If an antimicrobial usage measurement is particularly high compared to other farms it suggests higher levels of disease or an inappropriate treatment approach. From this, methods can be implemented to try and reduce antimicrobial usage levels.

The next step will describe a case study where benchmarking has been particularly useful.

Please find a downloadable copy of the PowerPoint slides used in the video in the downloads section below.

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Antimicrobial Stewardship in Veterinary Practice

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