Animal transfer studies (Residues)

In certain situations, the use of a pesticide may leave significant residues in crops or crop parts that may be fed to animals. The possibility of these residues transferring from the plant material to the food-producing animals that may consume it needs to be addressed in registration applications.

The main purpose of this guideline is to assist you in determining the type of data you need to provide to us. Some situations will require a specifically designed animal transfer study, while in other situations, other data and argument may be used to address the transfer of residues to food-producing animals. This guideline is directed mainly at clarifying the difference between these 2 situations.

Relevant animal commodity maximum residue limits (MRLs) must be set for all situations where there is a reasonable likelihood of food-producing animals consuming plant material that has been treated with a pesticide. These MRLs should be based on either the animal transfer study or other data with argument. The level of data required will depend on the magnitude of the residues in the crop and whether the plant material concerned is a major animal feed. Relevant withholding periods for inclusion on labels should also be proposed (for further information, refer to the guideline on withholding periods). The MRLs should relate to the primary food commodities of animal origin (Codex Class B), which are referred to in this guideline as animal commodities.

1. Purpose of animal transfer studies

Animal transfer studies are designed to determine the highest amount of pesticide residue that is likely to occur in edible animal commodities (including meat, fat of meat, edible offal, milk and eggs) when animals consume a feed or forage crop or any plant parts used as animal feeds that contain significant residues of the pesticide.

2. When are animal transfer studies required?

Specifically designed animal transfer studies are required only when:

• significant residues (greater than 0.1 mg/kg in total animal diet) occur in crops or parts of a crop (such as trimmings or waste) fed to animals, and/or
• metabolism studies indicate that significant residues (greater than 0.01 mg/kg) may occur in any edible animal tissue or that there is potential for bioaccumulation of the pesticide. If metabolism studies have been conducted at dosing levels much higher than the anticipated dietary burden of animals, argument and other data may be presented to demonstrate that significant residues in tissues would not occur.

Therefore, to evaluate whether an animal transfer study is needed, you will need to generate adequate data on residues in the crop and/or crop parts and on animal metabolism.

3. Conducting animal transfer studies

Animal transfer studies may be necessary in both ruminants and poultry. Dairy cows are the preferred ruminant species, but lactating goats are an acceptable model. Hens are the preferred poultry type. A study on pigs may also be required if significantly different metabolites are present in ruminants, poultry and rats. Animal transfer studies should be conducted only in those species (or representative species) whose diet is likely to include feed containing the residues.

Guidance on conducting animal transfer studies is provided in the Food and Agriculture Organization of the United Nation’s guidelines on producing pesticide residue data from supervised trials and in the OECD Guidance Documents and Test Guidelines.

Particular attention should be given to the appropriate dosing levels. Guidance on the single dose and exaggerated dose (3 to 10 times the single dose) is given in the guidelines cited above. Generally, the single dose should be at a level that is representative of residue levels in potential animal feeds. Groups of animals (3 for large animals, 10 for poultry) should be dosed for 28 days.

Table 1 shows the minimum commodities that should be sampled for the various animal groupings.

Data on fish or on honey from bees should be presented where relevant.

In some cases, only incomplete data may be available (such as in an animal transfer study where only some edible animal components [meat, milk or eggs only] were analysed). If suitable argument can be made (for example, argument based on results of metabolism studies), consideration will be given to setting appropriate animal commodity MRLs.

For some chemicals and crops, a suitably designed and performed metabolism study may replace the need for at least one animal transfer study that would otherwise have been required (see Results of metabolism data).

4. Crop residue trials

Residue trials on crops consumed by animals will provide an initial indication of whether an animal transfer study is needed.

Applications of the pesticide should be made to the crop that will result in the maximum residues possible from the proposed use pattern. Therefore, treatments should be made at the maximum label rate and with the maximum number of applications according to the use pattern. Treatments should also be made at 1.5 and 2 times that rate.

You should give careful consideration to the timing of when the crop or crop parts may be grazed or fed to animals so that appropriate samples can be taken. Sufficient sampling points should be taken to show a residue decay curve. If a withholding period is necessary, the sampling regime must be spread across the time range within which the withholding period is expected to occur. It is essential to sample at the recommended withholding period; otherwise, the withholding period will be set at the next longest sampling time.

As a guide, for crops that may be grazed or fed to animals as a failed crop, appropriate sampling points for the crop or crop parts consumed by animals are:

• on the day of application (or at the earliest time after application that sufficient plant material exists for sampling)
• at the time of any proposed withholding period
• at least one point in between (unless the above sampling times coincide) and
• at least one point after the sample taken at the proposed withholding period.

If you are proposing an extended withholding period, additional samples should be taken at the time of the proposed extended withholding period. For crops of which a harvested portion, or the crop trash and stubble, is fed to or grazed by animals, appropriate samples for residue analysis should be taken at that time. Residues should be determined on a dry-weight basis. Moisture content should be reported to allow for plant material that is exclusively consumed in a green form.

The results from the crop residue trials are used to determine the relevant feeding levels for the animal transfer studies and for supporting proposals for MRLs in primary animal feed commodities.

Guidance on conducting crop residue trials is provided in the residues section of the regulatory guidelines, the Food and Agriculture Organization of the United Nations guidelines on residue trials and in the OECD Guidance Documents and Test Guidelines.

5. Plant material consumed by animals

We are currently developing a definitive list of crops that could be consumed by food-producing animals.

Specifically-designed animal transfer studies should only be considered for treated crops if it is an accepted practice for the crop or crop parts to be consumed by food-producing animals and significant residues are present in the primary animal feed commodity or there is potential for bioaccumulation.

Crops that are rarely or only occasionally consumed by animals will not require specifically designed animal transfer studies. However, to allow for regulatory monitoring, MRLs should be proposed based on appropriate metabolism data (see Results of metabolism data). It is up to you to provide suitable information and argument to demonstrate whether any crop material is fed to animals and, if so, what contribution it makes to the animals’ total diet. If no appropriate data are submitted, a label restraint about grazing/feeding will be required for these crops (see Use of label restrictions).

6. Significant residues in animal diets

A practical limit for significance is considered to be 0.1 milligram per kilogram of the animal’s total diet and/or 0.1 milligram per kilogram for animal feed commodities that form significant parts of the animal’s diet, such as certain pulses, cereal grains, oilseeds, legume animal feeds, pastures and straw, fodder (dry) and hay of cereal grains and other grass-like plants. As animal diets do not consist solely of the crop or crop part under consideration, allowance must be made for the maximum proportion it may contribute to the animal’s diet. The maximum amount of residue in the animal’s total diet can be estimated by multiplying the residue level found in the crop (at the earliest time it may be consumed by animals) by the maximum proportion it would represent in the diet. There is no need to conduct animal transfer studies if:

• the dietary consumption level for animals is below 0.1 mg/kg
• the metabolism data do not indicate that significant residues (greater than 0.01 milligram per kilogram) may occur in edible tissues
• there is no potential for bioaccumulation.

The dietary contribution of various feed components should be carefully considered so that realistic dietary figures are used. These figures will need to be justified by the applicant.

7. Use of label restrictions

In some circumstances, you may be able to include label restrictions that limit the exposure of livestock consuming plant material containing significant pesticide residues. You can do this either by including on the label a longer than normal withholding period to allow the residues to dissipate to insignificant levels, for example:

Do not graze or cut for stock food for [x] weeks after application. 

Or, by prohibiting animal consumption of the treated crop, for example: 

Do not graze any treated area or cut for stock food. 

Do not feed [produce/grain] harvested from treated areas to food-producing animals including poultry.

If you are proposing an extended withholding period, you must substantiate the proposal with data and/or argument.

The use of label restrictions is only appropriate if they are feasible under normal agronomic practices – that is, in situations where the grower is able to directly control animal access to the crop or crop parts and where the economic value of the animal feed commodity is not so great as to make the restriction impracticable.

8. Results of metabolism data

Metabolism and degradation studies in animals are usually conducted using radiolabelled materials since this allows labelled compound and transformation products (metabolites) to be distinguished readily from natural biological constituents. The studies elucidate the nature of the residue present and where they are distributed within the animal; the degradation products can then be assessed in terms of their toxicity and whether they constitute a major or minor constituent of the total residue of potential concern.

Metabolism studies conducted at a dosing level closely approximating, or higher than, the potential livestock dietary consumption of the particular residue can be used to assess whether an animal transfer study is required. If the metabolism data show that significant residues may occur in any edible animal commodity, animal transfer studies are required. For metabolism studies conducted at dosing levels much higher than the potential livestock diets (as determined in the crop residue trials), if warranted, argument and other data may be presented to demonstrate that significant residues in tissues would not occur.

For crops that are occasionally consumed by animals or when metabolism data has shown that the compound has no potential for significant residues in animals, a specifically designed animal transfer study is not required. In these situations appropriate animal commodity MRLs may be established based on the results of metabolism studies.

A metabolism study on a lactating goat may be used to set MRLs for meat, fat of meat, offal and milk, provided the dosing in the metabolism study represents a close approximation of or exceeds the likely dietary consumption of the pesticide. Dosing should take place for at least 7 consecutive days and residue levels should have either dissipated or plateaued. A similar study in poultry may be used to set MRLs for poultry meat, fat of meat, offal and eggs.

9. Proposals for animal commodity maximum residue limits and withholding periods

Proposals for MRLs for relevant edible animal commodities (for example, meat, milk and eggs) and appropriate withholding periods should be given in a registration application. The proposals should be sufficient to cover the maximum residue levels likely to occur as shown in the animal transfer and/or metabolism studies. Proposals for MRLs are also needed in primary animal feed commodities.

If it can be clearly demonstrated that residues are not present in animal feed commodities, MRLs can be recommended ‘at or about the limit of analytical quantitation’ in animal commodities. In this case you will need to propose this level. For further information, refer to the guideline, Maximum residue limit proposals ‘at or about the limit of analytical quantitation’.

Whenever animal commodity MRLs are proposed, a suitable analytical method is required for determining residues in the animal commodities concerned.

10. Further reading 

The following documents may also provide assistance in developing appropriate data.

Commission of European Communities, 1993, Guidelines for the establishment of community maximum residue levels (MRLs) of plant protection products in food and feedstuffs of plant and animal origin, Appendix F: Metabolism and distribution in domestic animals; and Appendix G: Livestock feeding studies. Directorate-General for Agriculture, Brussels, January 1993.

Commission of European Communities, 1993, Study concerning the inclusion of active substances, in Annex I to Council Directive 91/414/EEC: Residues in or on treated products, food or feed, Directorate-General for Agriculture, Brussels, January 1993, pp. 91–6.