KEY POINTS

  • Backyard poultry are technically food-producing animals
  • Where medicines are prescribed under the cascade, only medicines listed in the Table of Allowed Substances should be used
  • Withdrawal periods for the cascade use of medicines should take into account the withdrawal periods for the species in which the product is authorized, along with the fact that a chicken or duck’s ovary contains approximately 14 egg yolks, all at various stages of development

Over the past decade, small-scale poultry keeping has increased dramatically. Many of these new keepers view their poultry as pets rather than farmyard animals. However, irrespective of the purpose for which poultry are kept, they are technically ‘farm animals’ and ‘food-producing animals’. Unlike in horses, there is no current provision allowing for poultry to be classed as non-food producing animals. This has implications for medicating such birds and for their disposal after death.

Poultry

There does not appear to be a definition of poultry in the Veterinary Medicines Regulations (VMR), but there is under other UK legislation.

The Avian Influenza (Preventative Measures) (England) Regulations 2006 defines poultry as: all birds that are reared or kept in captivity for the production of meat or eggs for consumption, the production of other commercial products, for restocking supplies of game or for the purposes of any breeding programme for the production of these categories of birds.

The Diseases of Poultry (England) Order 2003 defines poultry as: domestic fowls, turkey, geese, ducks, guinea fowls, quails, pigeons, ratites and pheasants and partridges reared or kept in captivity for breeding, the production of meat or eggs for consumption or for restocking supplies of game.

There are a great number of medicines (antimicrobials) authorized for use in poultry, all of which have meat withdrawal periods that can be easily followed. For male birds and turkeys, the use of any of these medicines is straightforward. However, for egg-laying chickens or ducks, the majority of authorized products state that they ‘should not be given to birds producing eggs for human consumption’.

For commercial laying flocks, products with a zero-day egg withdrawal are almost exclusively used. These products tend to have a relatively narrow spectrum of activity, and any birds failing to respond are humanely euthanased. For general practitioners dealing with pet chickens, such an approach would be unthinkable.

When treating backyard poultry, before any medication is prescribed under the cascade, the veterinary surgeon must ensure that the active ingredient(s) are listed in the Table of Allowed Substances in Commission Regulation (EU) No 37/2010.

Defining birds as producing eggs for human consumption

Classifying whether or not birds are producing eggs for human consumption is difficult. It is debatable as to whether or not prepubescent chickens can be considered as egg-laying hens. Some preparations of doxycycline currently authorized in the UK state that they should not be used within 14 days of the onset of egg laying; however, in the Table of Allowed Substances in the EU, there is a side note stating doxycycline should not be given to birds producing eggs for human consumption. As such, it may be argued that pullets before the onset of lay are not producing eggs for human consumption at the time of treatment.

For owners using their eggs for hatching rather than eating, there may be a case to argue that such birds are not producing eggs for human consumption. Furthermore, owners could potentially argue that they will never eat eggs from a treated bird. However, if the poultry are re-homed or sold (as frequently happens with breeding birds), their new owners may not be aware that any eggs from their new birds should not be eaten.

Antimicrobials

The majority of antimicrobials authorized for use in poultry do not have established Maximum Residue Limits (MRLs) for eggs. Furthermore, many of these antimicrobials have explicit notes in the Table of Allowed Substances to explain that they are not to be used in birds producing eggs for human consumption.

Before the cascade use of any product, the prescribing veterinary surgeon must ensure that there is no authorized product to treat the patient’s condition. For non-egg producing birds, there are a sufficient number of products available with meat withdrawal periods. For laying birds, the prescribing veterinary surgeon must first try to use a product with a defined MRL for eggs.

Antimicrobials with a defined MRL for eggs
Products with a defined MRL in eggs   Spectrum of activity
Chlorotetracycline 200 µg/kg Mycoplasma, Salmonella, Escherichia coli, Pasteurella and Clostridium perfringens
Colistin* 300 µg/kg E. coli (poor intestinal absorption)
Erythromycin 150 µg/kg Mycoplamsa, Pasteurella and E. coli
Lincomycin 500 µg/kg Staphylococcus, Erysipelothrix, Mycoplasma and Clostridium perfringens (poor intestinal absorption)
Neomycin 500 µg/kg E. coli (poor intestinal absorption)
Oxytetracycline 200 µg/kg Mycoplasma, Salmonella, E. coli, Pasteurella and Staphylococcus
Phenoxymethylpenicillin* 25 µg/kg Clostridium perfringens
Tiamulin* 1000 µg/kg Mycoplasma and Brachyspira
Tylosin* 200 µg/kg Mycoplasma and Clostridium perfringens

* Antimicrobials currently authorized in the UK with zero-egg withdrawal preparations available.

If none of the products in this table are suitable, then the prescribing veterinary surgeon must use the cascade to prescribe either a product authorized to treat another condition in the same species or a product authorized to treat the same condition in another food-producing species.

See also the Prescribing cascade.

The following table details antimicrobials in the Table of Allowed Substances that have no MRL for eggs but do not specifically indicate that they are not to be used in birds producing eggs for human consumption. Only currently available antimicrobials in the UK have been listed.

Antimicrobials allowed in food-producing animals in the UK with no specific prohibition for use in birds producing eggs for human consumption
Products with no MRL for eggs but do not indicate 'do not use in bird producing eggs for human consumption' Spectrum of activity
Marbofloxacin Mycoplasma, Salmonella, E. coli, Pasteurella and Staphylococcus
Cefquinome Mycoplasma, E. coli, Pasteurella and Staphylococcus
Ceftiofur E. coli and Pasteurella (poor intestinal absorption)
Gamithromycin Pasteurella
Tulathromycin Pasteurella and Mycoplasma

There are some products for which an MRL cannot be established and therefore must not be used in any food-producing animals, as listed in the following table.

Products for which an MRL cannot be established (Annex 4)
Chloroform
Chloramphenicol
Chlorpromazine
Colchicine
Dapsone
Dimetridazole
Metronidazole
Nitrofurans (including furazolidone)
Ronidazole

Anticoccidials

There are two currently authorized anticoccidial agents in the UK: toltrazuril and amprolium. Toltrazuril has no MRL for eggs and states that it should not be used for birds producing eggs for human consumption. As coccidiosis usually affects poultry before the onset of egg laying, then technically the affected birds may not be considered as birds producing eggs for human consumption.

Amprolium does not require an MRL and can be used in laying chickens with a zero-day egg withdrawal.

Anthelmintics

Currently, fenbendazole and flubendazole are authorized in the UK with an established MRL for eggs. There are preparations of both with zero-day egg withdrawal.

Ectoparasite treatments

There are a number of ectoparasite treatments listed in the Table of Allowed Substances with no MRL for eggs. Most of these do not prohibit their use in birds producing eggs for human consumption. However, it must be ensured that any treatments considered are listed in the Table of Allowed Substances, as a number of products authorized for small animals, such as fipronil, are not.

Other veterinary products

For other veterinary medicines, such as analgesics, there are no currently authorized products for poultry in the UK. Almost all of such products have no MRL for eggs, but also do not prohibit their use in birds producing eggs for human consumption.

Setting an egg withdrawal period

When setting withdrawal periods under the prescribing cascade, the minimum withdrawal period for eggs is 7 days and for meat is 28 days. However, the Veterinary Medicines Directorate (VMD) guidelines also state that consideration must be given to the withdrawal periods set for other species. For example, a milk withdrawal period may be used as a guide when setting an egg withdrawal period. Additionally, consideration must be given to avian physiology; laying hens and ducks tend to have at least 14 days’ worth of eggs developing in their ovary.

In practice, the meat withdrawal set for products used under the cascade should either be 28 days or identical to the meat withdrawal period for the authorized (food-producing) species (whichever is longer).

With regard to egg withdrawal periods, they should be a minimum of 7 days, but if there is a milk withdrawal period, this should be used as a guide, with 15 days added on to take into account the developing egg yolks.

Where a product is being used ‘off-label’, it is advisable to have the owner sign an informed consent form.

Note

Owners selling eggs must keep a veterinary medicines record book.

Backyard poultry quiz

1. Which of the following best describes the status of backyard poultry as food producing animals?




2. Which one of the following statements is true?




3. A client presents a pet chicken with lice and the veterinary surgeon wants to use a spot-on treatment. What should they do next?




4. The veterinary surgeon decides to use a cattle product in a pet laying hen, under the cascade, for which there is a 15 day milk withdrawal. What should be the egg withdrawal set?




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