Why In-Feed Antimicrobials?

Introduction

Like humans, animals can become ill and many need treatment for a bacterial infection. In this situation a veterinary surgeon may decide a course of an antibiotic.

Why treat?

In modern livestock production, animals are normally kept under environmental conditions which are as balanced as possible to assist health protection and growth. This means that there are often large numbers of livestock in the same protective environment.

If disease affects these animals, the pattern is that a small number may be clinically infected, others may be incubating the disease whilst the third group may be infected but not yet developing the disease. Because it is impossible under normal conditions to differentiate between these latter groups it is normal to give therapeutic treatment to all the affected and in-contact animals (sometimes technically termed "metaphylaxis").

It is often forgotten that for the livestock producer, the use of antibiotics is a last resort. There is no NHS for animals and the use of such products is very expensive for farmers. Therefore, their main interest and that of their vet is to use every other possible avenue to prevent and control infection before it can devastate their animals and cause significant loss.

Why in-feed?

For very small groups of animals or animals kept individually it is possible to use individual oral dosing of the animals or to inject the animals with the appropriate dose of antibiotic. With larger groups of livestock this becomes impractical and therefore other dosing systems are essential.

Where individual dosing of animals becomes impractical, the only systems that are suitable for large groups are drinking water medication or in-feed medication. Many producers prefer water medication but this usually requires a relatively complex system of dosing apparatus and ensuring that the water supply line and tanks are free of any matter that may cause deterioration of the active ingredient.

Particular attention has been focused on the administration of substances “in-feed”. It is important to remember that there are many positive, animal-friendly, reasons for supplying medicines in this way:

Freedom from stress - compared to injection or oral dosing, there is no stress to animals or staff - in major groups individual dosing would be a mammoth exercise, probably resulting in injuries and death.
Universal suitability - while other systems, such as water medication, can be very effective in some units, only in-feed medication is equally appropriate to all sizes of unit and all types - intensive or extensive.

For all the above reasons the use of in-feed medication is still the most widely used and has fewer management problems than other systems. In the presence of disease, or where disease is suspected, or based on previous experience the disease is imminent, the veterinary surgeon supplies a prescription to the feedstuff manufacturer and the appropriate medication can be supplied during the manufacture of a special batch of treated feed.

What controls?

Before an antibiotic is allowed to be marketed for animal use, it has to be approved according to very strict European criteria on its quality, efficacy and safety.

Growth promoting antibiotics (sometimes known as digestive enhancers) are not permitted for use in the EU: the category within the legislation under which they used to be authorised was removed on 1 January 2006.

Antibiotics are available only with the authorisation of the veterinary surgeon. The difficulties of administration to groups of animals, as explained above, have meant that a high proportion of therapeutic antibiotics for livestock are supplied in the feed.

All premises that are involved in this incorporation are licensed for the purpose and are subject to inspection. Similarly, the veterinary surgeon and the farmer have to ensure that there are full records of usage of antibiotics, which again are subject to inspection.

As a result of all these checks and balances the illegal use of any in-feed antibiotic in the UK is negligible and this is also controlled by a comprehensive surveillance of residue levels in tissues. In the UK, as distinct from many other countries in the EU, these residues data are published on a frequent basis and the number of samples that show levels below the action limit, known as the Maximum Residue Limit (MRL), is remarkably good, over 99.5%.

Nevertheless, the animal health industry has shown a leadership role in the responsible use of antibiotics and along with the World Veterinary Association and the International Federation of Agricultural Producers, the Global Animal Health Industry Association (COMISA) (now International Federation for Animal Health (IFAH)) produced a set of prudent use guidelines in 1999. This has been followed in the UK by a set of guidelines from the consortium of farming, veterinary, supply chain and consumer organisations specifically set up to promote the Responsible Use of Medicines in Agriculture (RUMA).

Since its establishment in 1997, RUMA has been working on and published species specific guidelines on the use of antibiotics. These have been updated in 2004 (short version for farmers) and 2005 (long version primarily for veterinary surgeons). All parties are committed to the concept of responsible use rather than across the board reduction of use. The aim is, by encouraging best practice in animal husbandry, to reduce the need for antibiotic treatment.

What about resistance?

In recent years there has been increasingly vociferous concern expressed about the use of antibiotics in livestock. This has been linked to the increasing levels of antibiotic resistance in man. However, it is clear that the main bacteria which are of concern in human medicine are unrelated to bacteria which are found in animals and in most cases animals are not the source of human problems.

Where resistant bacteria could be theoretically passed from animals to man, risk assessment studies are showing that the risk to man is very small, probably much less than driving to work or crossing the road.

Much of the resistance to antibiotics in man is hospital derived, where the patient has received the resistant infection during hospitalisation, and the bacteria have developed resistance as a result of antibiotic usage within that hospital environment and not as a result of antibiotic use elsewhere.

Conclusion

Antibiotics used in feed are a precious resource and, if used responsibly, will continue to assist in the provision of healthy, affordable food for the human population. Administration in feed provides an ideal way to treat groups of animals, extensive or intensive, and is subject to extensive regulation.

Although there is much concern about the development of resistance to antibiotics, careful, judicious use of these products will prolong their life and that of the recipients. The most widely used class of antibiotics in animal populations are those that were the first discovered 50 years ago. It is tempting to speculate why this is so, and why resistance is not a major threat to most livestock populations. Perhaps it is because most livestock are only a few weeks, or months, of age when they are processed for food. Any resistant bacteria, in the main, disappear from the farm and the next batch of animals is populated by totally susceptible bacteria. This process contrasts markedly with the situation in the human population where carriers of resistant organisms may remain in the community for a very long time.

Finally, the livestock producer has gone to great lengths to provide optimum environmental and disease control measures to minimise the possibility of disease in his animals or poultry. There is no substitute for the highest possible standards of husbandry and, providing they are allowed to compete on equal terms with the rest of the world, the UK producer will use in-feed antibiotics in the most responsible way, ably assisted by their veterinary surgeon.

Updated October 2007

For information on anticoccidials see NOAH briefing document 13 - Anticoccidials)