TABLE 5:

Definitions for different metrics for presenting antimicrobial (AM) use including calculations, data required and pros and cons for each

MetricCalculationRequirementsProsCons (including assumptions)Reference
Total mgs= (Total mls, number or kg of product sold or used) x (mg/ml, mg/unit or mg/kg)
  • Total mg of each active substance used

  • Simple

  • Ignores variation in animal size/weight and number of cattle

  • Does not take into account different dose rates and course lengths across AMs

-
Total mg/kg
(sometimes called mg/PCU if the standard weight of 425 kg is used)
=Total use (mg)/total wt of cattle at risk of treatment (kg)
(total use (mg) defined as above)
  • Total mg of each active substance used

  • Number of cattle at risk of treatment

  • Cattle weight (can be ESVACdefined (425 kg) or country-specific or unit-specific)

  • Simple

  • Takes into account animal weight and number of cattle

  • If using standardised weights these may not be accurate for the unit in question

  • Does not take into account different dose rates and course lengths across AMs

6
Daily dose metrics
(eg, DDDvet)
=Total use (mg) / (daily dose (mg/kg) x total weight of cattle at risk of treatment (kg))
The calculation is carried out for each AM category and added together to get the total figure.*
  • Total mg of each active substance used

  • Daily dose per kg*—these can be ESVAC-defined, or country-specific or unit-specific

  • Number of cattle at risk of treatment

  • Cattle weight (can be ESVAC-defined (425 kg) or country-specific or unit-specific)

  • Takes into account animal weight and number of cattle

  • Takes into account dose rate differences across AMs

  • ESVAC-supported

  • Dose and cattle weight can be made specific to country or unit which improves accuracy and comparability

  • More complicated to calculate than mg and mg/kg metrics

  • If using standardised weights and/or defined dose rates, these may not be accurate for a particular country or unit

  • Assumptions rely on knowledge of certain aspects of medicine pharmacokinetics that are not necessarily known (eg, the exact duration of action)

  • Does not take into account different course lengths across AMs

  • Some drugs or routes of administration do not have defined dose values

11
Course dose metrics
(eg, DCDvet)
=Total use (mg) / (course dose (mg/kg) x total weight of cattle at risk of treatment (kg))
The calculation is carried out for each AM category and added together to get the total figure.
  • Total mg of each active substance used

  • Daily course per kg—these can be ESVAC-defined, or country-specific or unit- specific

  • Number of cattle at risk of treatment

  • Cattle weight (can be ESVAC-defined (425 kg) or country-specific or unit-specific)

  • Takes into account animal weight and number of cattle

  • Takes into account dose rate and course length differences across AMs

  • ESVAC-supported

  • Dose, course and cattle weight can be made specific to country or unit which improves accuracy and comparability

  • More complicated to calculate than mg and mg/kg metrics

  • If using standardised weights and/or defined dose rates and course lengths, these may not be accurate for a particular country or unit

  • Assumptions rely on knowledge of certain aspects of medicine pharmacokinetics that are not necessarily known (eg, the exact duration of action)

11
Cow calculated courses (CCC)=Number of courses in 12 months / number of cattle on the holding
  • Number of courses used on the farm (calculated from quantity of each medicine used on farm and the quantity required per course)

  • Number of cattle at risk of treatment, split into youngstock (<24 months) and adult (>24 months)

  • Takes into account number of cattle and can use specific weights

  • Takes into account course differences across AMs

  • Takes into account youngstock use (and can separate use in youngstock from use in adults)

  • Requires information on the number of youngstock as well as the number of adult dairy cattle

  • If using standardised weights (100 and 600 kg) and/or defined dose rates and course lengths, these may not be accurate for a particular country or unit

  • Medicines are assigned only for youngstock or only for adults, which may not be accurate

T. Clarke, personal communication
  • *Rather than dose per kg liveweight, lactating cow tubes are dosed at number of tubes per cow per day, dry cow tubes are dosed as '4 per cow' as a single treatment and intrauterine products are one unit per cow.