Withdrawal periods for chickens, eggs and turkeys

On the basis of the determination below, the withdrawal periods for chickens, eggs and turkeys were recently assessed and set in the United Kingdom at:
 

Chickens - may be slaughtered for human consumption only after 2 days from the last treatment.
 

Eggs - Nil (zero) withdrawal period for eggs
 

Turkeys - may be slaughtered for human consumption only after 5 days from the last treatment.
 

Birds must not be slaughtered for human consumption during treatment.

The determination of withdrawal periods for edible tissues is a complex affair, but considered essential to protect the safety of the consumer of poultry meat and eggs.
 

In the European Union (EU), there is a process to establish withdrawal periods, especially for microbiologically active products, such as tiamulin.
 

Firstly from a series of required toxicological studies a 'No observed effect level' (NOEL) is established, where administration of a certain dose of a product has absolutely no effect on the animal, either clinically, toxicologically or biochemically.
 

This is used to determine the 'Acceptable daily intake' (ADI) of the product which may be consumed by a human being. The NOEL is divided immediately by a safety factor of 100 to give extra assurance for human consumers.
 

This gives a Toxicological ADI as it is based on toxicological study calculations. For antimicrobial substances there is an additional safety assessment to determine a Microbiological ADI, based on the effect of the substance on the normal gut bacterial flora found in humans. The lowest ADI, whether toxicological or microbiological, is then used to determine the level of a substance that can be ingested in either an edible meat tissue or egg without causing any adverse effect on the consumer either toxicologically or on their gut flora. A toxicological ADI is used for tiamulin.
 

The levels that can remain in tissues are called the 'Maximum residue levels' (MRLs). These levels are set for all medicinal products used in animals for human consumption in the EU. The time it takes for the residues to fall below the MRL after treatment, determines the withdrawal period required before animals can be sent for slaughter and used for human consumption.
 

NOEL for tiamulin	- 3mg/kg bodyweight
ADI (toxicological) of tiamulin in a 60kg man	- 1.8mg/day
ADI (microbiological) of tiamulin in a 60kg man	- 1.92mg/day

Maximum residue levels (MRLs)
Marker residue Animal species MRLs (µg/kg) Target Tissue Sum of metabolites that may be hydrolysed to 8--hydroxymutilin Chicken 100 100 1000 Muscle Skin + fat Liver Tiamulin Chicken 1000 Eggs Sum of metabolites that may be hydrolysed to 8--hydroxymutilin Turkey 100 100 300 Muscle Skin + fat Liver