As outlined by Mills et al. (2018), there are several types of data that can be used, but different producers must collect the same data components so that the information can be compared between farms. There are also different ways of adjusting the data to account for the weight of animals being treated, the number of days in the production cycle, and the type of antimicrobial being used.
Here are some examples of different metrics that can be used to measure antimicrobial use^{8}:

1. Total mg
Total mg = (total mls, number or kg of product sold or used) x (mg/ml, mg/unit, or mg/kg of active ingredient) 
 Likely the simplest metric to use
 Ignores the size/weight of the animals as well as the number of animals that are on the farm. Therefore, you can’t compare farms with different numbers of animals or farms that raise different age classes of animals
 Doesn’t take into account different dose rates and lengths of treatment

 As such, this metric may be lower for antimicrobials of the highest importance, which tend to be more potent and given in smaller volumes, but which may have a greater impact on the emergence of AMR.

2. Total mg/kg
Total mg/kg = total mg of antimicrobials / total weight of animals at risk of treatment (kg) 
 Another simple metric that takes into account the animal weight and number of animals
 It may be difficult to get individual weights on each animal, but using standardized weights may not be accurate.
 In addition, different antimicrobials are used in different age classes of animals
 Using an inaccurate weight for the animals at risk of treatment would lead to an over or underestimation of actual antimicrobial use in mg/kg as shown in the table above
 Does not take into account different dose rates and course lengths across different antimicrobials
 As such, this metric may be lower for antimicrobials of the highest importance, which tend to be more potent and given in smaller volumes, but which may have a greater impact on the emergence of AMR
 For example, Ceftiofur (Excenel, Zoetis) is dosed at 6.6 mg/kg in cattle, whereas long acting oxytetracycline (Oxyvet 200 LA) is dosed at 20 mg/kg in cattle
Here is an example calculation below for 2 farms of similar numbers of animals with differing sizes:
Farm

Total mg of antimicrobial used

Number of beef cattle

Mean cattle weight (kg)

Total mg/kg using meancattle weight for each farm

Total mg/kg using standardized weight of 300 kg^{10}

Farm 1

2,000,000

200

700

14.3

33.3

Farm 2

2,000,000

200

400

25

33.3


3. Defined Daily Dose (DDD)
DDD = total use (mg) / (daily dose (mg/kg) x total weight of cattle at risk of treatment (kg)) 
 This calculation can be carried out for each antimicrobial category and added together to get the total amount
 Can be calculated using mg/kg/d (ddd) where each kg of the animal is taken into consideration or using g/animal/d using standardized weights (DDD)
 There are several advantages to using this metric including:
 Accounting for animal weight and number of cattle
 Accounting for dose rate differences across different antimicrobials
 Also used by several countries and is a defined metric in Canada with specific calculations for broiler chickens and turkeys^{9}, pigs^{9}, and cattle^{10}
 This can allow comparison between different countries
 This metric is more complex than the previous two, and has some additional limitations including:
 If using standardized weights or defined dose rate, they may not be completely accurate
 Some routes of administration for specific drugs do not have defined dose values
 Doesn’t take into account the number of courses an animal receives

4. Course dose metrics
Course dose metric = total use (mg) / (course dose (mg/kg) x total weight of cattle at risk of treatment (kg))

 This calculation is carried out for each antimicrobial category and added together to get the total amount
 Can be calculated using mg/kg/course (dcd) where each kg of the animal is taken into consideration or using g/animal/course using standardized weights (DCD)
 The advantage of using this metric over DDD is that it assigns the number of courses an animal receives and takes into account the daily dose and the course length
 It is also supported by several countries and is a defined metric in Canada with specific calculations for broiler chickens and turkeys^{9}, pigs^{9}, and cattle^{10}
 This can allow comparison between different countries
 It has similar limitations to DDD, however, as mentioned above it takes into account the course of treatment