This Belgian study collected the antimicrobial usage of a convenience sample of 57 Belgian dairy herds with an average of 69 lactating cows per herd. Data were collected by using the "garbage can audit"", asking the farmers to throw away all empty drug vials and tubes used to treat adult dairy cattle into these cans. This method is considered the most reliable for this pupose, as it reduces mistakes in registration of drug administration and at the same time allows between-herd comparison and identification of risk factors.