Course: Poultry diseases and pests | Last Updates: 7th October 2015
Concerns about the use, and perceived overuse or misuse of medicines in farm animals have been identified for many years by a number of scientists, interest groups and other commentators. They often refer to the possible pitfalls such use may have in terms of animal health and welfare, as well as food safety.
The problem areas mostly concentrate on the possibility of the development of drug-resistant organisms (so called "superbugs") or the possibility of medicine residues in meat, milk or eggs.
Poultry producers are well aware of their responsibilities in this area in observing the necessary withdrawal periods, after giving any medication in feed or water, to avoid unacceptable residues in poultrymeat and eggs. However, residues may still be detected and there is always room for improvement.
In the UK, the Veterinary Medicines Directorate (VMD) oversees the authorisation and use of veterinary medicines in all animals. In relation to residues, the VMD operates surveillance programmes to monitor various foods for the presence or absence of residues to ensure the correct use of veterinary medicines and safeguard consumer safety.
Samples are collected on farm or at the abattoir. The most up-to-date results, published for 2007, show that in the National Surveillance Scheme for domestic produce, 38,749 analyses were carried out on animal tissues. But only in 49 cases were residues of veterinary medicines detected at concentrations above EU or internationally agreed limits.
But there is no room for complacency and it is important that monitoring continues and that the results are subjected to independent review. Therefore, as well as publishing all its results, in 2001 the VMD set up an independent advisory committee, the Veterinary Residues Committee (VRC), to advise DEFRA ministers, VMD and the Food Standards Agency on the incidence and significance of residues of veterinary medicines in food.
Not only does the committee oversee the government’s statutory testing required under EU legislation, but also recommends testing that needs to be done under the UK non-statutory surveillance system. Testing for residues takes place on the "food we eat" and can be sampled from retail outlets, wholesalers or at Border Inspection Posts for imported food coming into the UK.
What is being tested for?
Testing is carried out for residues of antibiotics, coccidiostats, wormers, heavy metals, and hormones. There is a separate committee that looks for pesticide residues.
A residue is a trace of a substance that remains in a tissue or food after the animal has been slaughtered, or may be in the milk or eggs produced by an animal that has been treated. Medicines work by distributing themselves around the body so that they can reach the tissue where it is needed.
After a certain period of time, that medicine is either used up, broken down or removed from the body. All medicines authorised for use in food animals have to be assessed for how long its residues may remain in meat, milk or eggs and a withdrawal period is set. This is the length of time that must elapse after the end of treatment before that animal is slaughtered or its milk or eggs can be used for human consumption.
The residue testing is not looking for absolute zero in every case, as this is just not possible nor necessary. Rather, it is looking to ensure that any residue that might be present in food is below a level that may be harmful to consumers. Therefore, every medicine destined for use in food animals is assessed by scientific experts for the setting of a Maximum Residue Limit (MRL).
For medicines for which the experts see a need for setting an MRL, this is based on making sure that the consumer does not exceed the acceptable daily intake (ADI) for that medicine. This needs to consider how much of the substance might occur in each food eaten and how much of a particular food may be eaten each day by an "average" person.
MRLs are then set so that even if all of the foods consumed contain residues at the respective MRLs, the ADI will not be exceeded. Finally, the withdrawal period is then set to make sure that any residues are below the relevant MRL. The UK surveillance system then checks to make sure that these MRLs are not exceeded in animal tissues at slaughter and in food on sale to consumers.
What does this testing mean for the poultry industry?
The incidence of residues of veterinary medicines in food and food products remains extremely low and in recent years, only two where significant numbers of residue have been identified. These were nicarbazin in broilers and lasalocid in eggs. Both these substances are in-feed coccidiostats used to prevent coccidiosis.
In terms of lasalocid, this is another "good news" story for the industry and regulators. The problem was identified by the government monitoring system, results were fed back to the industry and through co-operation between VMD, the Food Standards Agency and the egg industry, the incidence has fallen dramatically.
That leaves us with nicarbazin in broiler liver, which has been more difficult to crack. Progress has still been made; indeed since 1998 the incidence of nicarbazin residues in chicken liver detected by the National Surveillance Scheme fell from a level of 25.5% to 8.5% in 2006. However, since that time the success has slowed with a low, but stubbornly persistent, number of non-compliant samples being detected each year.
An important part of the monitoring process is that each non-compliant sample is followed up, and in most cases a government veterinary visit and investigation is taken back to the farm of origin. These investigations have usually found that the necessary withdrawal period had been followed.
However, feed management problems such as possible previous feed spillages and presence of medicated feed in the litter or problems with feed holding up in bulk bins are often suspected, although this may be difficult to confirm retrospectively. Interestingly, most investigations demonstrate very good record keeping on medicine use by producers.
So what can broiler producers do?
The Food Standards Agency considers that the levels of nicarbazin found in British chicken do not pose a significant food safety health risk, but recognises that consumers expect these residue levels to be kept to a minimum, especially where they are avoidable with good farm practice.
To this end, the FSA has re-issued management advice (see right, bottom box) in a leaflet endorsed by the industry. By following these simple rules, producers will further improve the already good record that the industry has in producing food free of harmful residues.
Withdrawal Period The length of time that must elapse after the end of treatment with a medicine before slaughter or its milk or eggs consumed.
Maximum Residue Limit (MRL) The maximum concentration of a residue that is legally permitted or acceptable in or on a food. When determining MRLs, the Acceptable Daily Intake (ADI) must not be exceeded after considering intake from all sources.
Acceptable Daily Intake (ADI) An estimate of the amount of a substance that can be safely ingested daily over a lifetime without appreciable risk to the consumer.
Tips on avoiding residues
- Order and use precisely the required amount of medicated feed
- Clear up all feed spillages
- If practical, run the feed bin empty at the end of the grower stage
- Ensure that withdrawal periods are observed with medicated feed
- Ensure no residual feed from previous crops is given five days before slaughter
- Sign up for training sessions (such as those run by Elanco)
- Keep accurate and up-to-date records on medicine use
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