Residues, withdrawal periods and maximum residue limits
Residue assessment determines when food from a treated animal may enter the food chain. Maximum residue limits define acceptable concentrations in food, while withdrawal periods allow residues to decline below those limits after treatment.
Maximum residue limits and consumer safety
A maximum residue limit (MRL) is the maximum residue concentration accepted in the EU in food from an animal treated with a medicine or exposed to a biocidal product used in animal husbandry. Food such as eggs, milk and meat from treated animals must not contain residues hazardous to consumer health, so active substances and their residues must be assessed before authorisation of a medicine for food-producing animals.
Active substances in biocidal products used in animal husbandry undergo a comparable safety assessment; residue evaluation and, where appropriate, an MRL are needed when the substance presents a particular consumer concern. The Committee for Veterinary Medicinal Products assesses residue safety.
MRLs for residues of an active substance and its metabolites are based on the acceptable daily intake and set for relevant food commodities, such as cattle tissues and milk or poultry tissues and eggs. Setting MRLs follows a separate registration procedure with its own dossier.
Withdrawal periods and depletion studies
A three-day milk withdrawal period for an antibiotic used to treat mastitis means milk is discarded during those three days and can re-enter the food chain on the fourth day after the last administration. The withdrawal period is the minimum interval between the last treatment and collecting animal products for human consumption. A residue-depletion study establishes how long the substance or its metabolites take to fall below the safe level or relevant MRL.
The same principle applies to meat from cattle, pigs, sheep, horses and goats, with MRLs set for individual edible tissues, usually muscle, fat, liver and kidney. To name dairy cows on a product label, an MRL must have been set for milk, potential drug residues in milk must have been examined and a withdrawal period calculated.
Depletion-study animals must represent the intended target species' breed, weight range and age. Calves cannot replace dairy cattle in a study for a product intended for dairy cows merely because calves are easier to handle or accommodate.
Immunological products
Residue studies are normally unnecessary for vaccines in livestock animals. Certain adjuvants or preservatives can nevertheless make residue-depletion studies necessary.
Dietary exposure assessment
Food of animal origin can contain residues of veterinary medicines, feed additives and pesticides. The European Medicines Agency (EMA) and the European Food Safety Authority (EFSA) use modelled human dietary exposure in the evaluations underlying legally binding MRLs. Their assessments share principles but use different scientific approaches and practices according to the source of the residue, which can produce different outcomes.
A joint EMA–EFSA report announced in January 2023 proposed a harmonised approach across veterinary medicines, feed additives and pesticides in food of animal origin.