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AgVetLink March 2004 - Special Issue for Veterinarians: Page 6

Withholding periods: FACT or FICTION?

Withholding periods define the ‘treatment to sale-of-produce period’

FACT

The withholding period (WHP) that appears on the label of veterinary medicines is the time for which a specified agricultural product must be withheld before entering the human food chain. It is defined as ‘the minimum permissible time between the last application of that veterinary medicine to an animal and the sale of the animal to slaughter, the sale of farmed fish or the sale of any milk, eggs, or honey from an animal for human consumption’.

Legally enforceable withholding periods can be set only by regulators

FACT

A WHP is the regulatory tool used by the ACVM Group to manage compliance with the residue thresholds as prescribed under the Agricultural Compounds and Veterinary Medicines (ACVM) Act 1997 or the Animal Products (AP) Act 1999. Although notified as part of the label content, any WHP is also considered to be a condition of registration for any veterinary medicine registered with one– it is a legally binding requirement for any user of that veterinary medicine to obey WHPs (with the exception of default WHPs, which will be discussed later).

Manufacturers have in the past and continue to recommend ‘withholding periods’ that are not based on regulatory requirements, e.g. to manage issues of product quality such as wool residues, which are outside the scope of the ACVM or AP Acts. During the update process the ACVM Group will ensure that such label information is grouped away from the regulatory (and therefore legally binding) WHPs that currently relate only to meat, milk, eggs, farmed fish and honey.

The residue thresholds prescribed in the ACVM Act are those defined in the domestic food residue standards alone

FICTION

Section 4 of the ACVM Act, which describes risks to be managed in association with the use of agricultural compounds, does state that registered uses must not result in breaches of domestic food residue standards. The primary domestic standard is the New Zealand (Maximum Residue Limits of Agricultural Compounds) Food Standards 2002. This document contains a list of the maximum residue limits (MRLs) that can be present in agricultural produce (meat, milk, eggs, honey and crops) sold in New Zealand.

However, one of the other risks that must be managed under the ACVM Act is ‘risks to trade in primary produce’. In consequence, the approved WHP for any veterinary medicine that is registered for use in animals that produce exportable food for human consumption will take into consideration any MRLs established by our major export markets. These MRLs are expressed through Regulations issued under the AP Act. Currently, only pig and poultry products are not exported to major overseas markets.

There is only one type of approved withholding period

FICTION

It is a requirement for registration that applicants provide residue data or equivalent information and technical argument to enable the establishment of a WHP. Such WHPs will therefore either be assessed (approved following analysis of residue trial data) or allocated (based on less data together with other information). These WHPs are the minimum treatment to harvest intervals to be followed by users of the products.

In some circumstances it is not possible for registrants to conduct residue trials to establish WHPs for all the possible food commodities. This is common for horse and sheep products where meat and milk WHPs respectively must be established by law. The horsemeat and sheep milk sectors are considered minor uses globally and the ACVM Group recognises that to require residue trials for affected products (i.e. all horse and sheep products) would probably result in effective products being deregistered for use or new products not gaining registration.

In the past, such insufficient data presentations were managed by including a statement ‘Not for use in animals producing meat/milk for human consumption’. However, under the current risk management regulatory model it is inappropriate to deal with the lack of residue data by way of a blanket ban on use in entire groups of animals and the restriction is no longer supportable. Instead, the ACVM Group has adopted a range of ‘default’ WHPs that will be approved under certain circumstances where residue data have not been provided (see ‘Default withholding periods’ on page 5 for a full list).

Another group of standardised WHPs has also been established. The WHPs are specific to named active ingredients when included in specified formulation types and indicated for the treatment of certain species. This is mostly of benefit for registrants who are seeking 

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