Pardon me. I think I misunderstood the interpretation.
In the poultry industry specifically--and it is different for beef and pork--when a flock is medicated it is on a flock basis. That's for two reasons. One is the feasibility of getting the medication into those birds, because they're housed in very large groups. The other is because of the design of the chicken. For most animals it's only a fecal-oral route for exposure to disease, but chickens also sample the environment from their cloaca. So we need to treat them as a flock or a population in order to get a handle on that disease.