4.2.2 Milligrams of antimicrobial ingredient adjusted for animal biomass

In animal health, there are rarely sufficient data available to calculate a DDD indicator, though this is recommended where possible. Instead, the OIE has proposed a standard unit of measurement for AMC in animals, which is the milligrams of antimicrobial ingredient sold per kilogram of animal biomass (mg/kg). Like the DDD, the mg/kg estimate aims to enable comparison in AMC between settings and over time. The mg/kg is a ratio of the two quantities below:

• The amount of antimicrobial ingredients sold in medicines intended for use in animals. This can be sourced from national customs and manufacture records and is compiled annually by national veterinary medicine regulatory authorities.
• The total amount of animal biomass (that is, the total weight of all animals). The unit ‘biomass’ was developed to counter the challenges of comparing AMC in every type of farmed animal, from horses to fish, and at different stages of the production cycle (such as from piglets, which weigh less than 2kg at birth, to butcher hogs, which typically weigh 70–100kg at the time they are slaughtered). There are differences in the body weight of common livestock animals between countries due to differences in breeds, nutrition and other factors. To enable standardised comparisons, the OIE publishes a reference table of standard animal biomass for different species averaged across different production stages. To calculate total biomass, you then multiply the total number of farmed animals per species (which can be obtained from a national livestock census and/or slaughterhouse records) by the reference biomass value.

There are other standard units of measurement of AMC in animals, such as ‘mg of antimicrobial ingredients per Population Correction Unit (PCU)’. Unlike the biomass measure used by the OIE, the PCU specifically takes into account differences in AMU at different production stages and takes into account the fact that the majority of AMU occurs in relatively young animals below their typical weight at slaughter. However, many countries do not have the data available to calculate PCUs. (More information [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] about this approach is available.)