|.............||Prudent Use of Antimicrobials : a
Poultry Specialist's View
Paul McMullin MVB DPMP MRCVS
BRITISH VETERINARY POULTRY ASSOCIATION
What is different about Poultry
Poultry production is based on a pyramid such as is illustrated in figure 1. At the apex of the pyramid is a very small population of elite breeding birds. Successive generations both within the primary breeding company and at the level of commercial farms means that 1 male selected by the primary breeder could theoretically contribute genes to up to 20 million broiler chickens. This can result in rapid dissemination of improvements in disease resistance.
Many of the classical infectious diseases which affect poultry have been solved by eradication programmes or vaccines. These greatly reduce the need for antimicrobial medication. The remaining disease problems tend to be complicated. Frequently they present as 'complexes' in which multiple environmental factors interact with management and various sorts of pathogens. Most commonly viral pathogens reduce host resistance, either by a direct immuno-suppressive effect or by damage to mucosae, and hence permit tissue invasion by 'normal' bacteria. Here the emphasis is on managing the problem by the identification and progressive reduction of risk factors.
The actions to be undertaken need to be adapted to the requirements of each production system, company and farm, and will constantly evolve in response to changes in the animals, the farms, disease status, the environment etc. The extent to which these individual topics can influence the need for antimicrobial will also vary from farm to farm. In general it is necessary to carefully co-ordinate activities under different headings in order to achieve the desired effect. Of particular importance is the establishment of good 'biosecurity' principles to avoid disease transmission between successive flocks and to prevent infections reaching flocks from the general environment. It must, however, be recognised that the 'thickness of the biosecurity shield' will tend to reduce as we move down through the levels of the production pyramid. Many measures applicable to elite breeding stock simply will not be feasible for final-generation stock because of the large number of birds and farms involved.
Therapeutic antimicrobial products should..
Demonstration of therapeutic prudence requires good documentation of medicine usage. This will include advisory work relating to on-farm recording systems. Specialist poultry practices will commonly hold a broad range of animal health-related information on which they can base treatment decisions. In our practice we have separate computerised systems dealing with health programming, farm visits and necropsy submissions, serological testing and microbiological testing. In addition we have simple computerised systems to document all medicines issued. A sample (fictitious) prescription is illustrated in figure 2 below. Note that a 'Human Food Residue Avoidance ' notice is included which shows the recommended withdrawal period for meat and, if appropriate, eggs.
Figure 2: Fictitious example of a medicine prescription for poultry
Feed Additive Antibiotics (Dir. 70/524) These compounds are not used under veterinary prescription, though their use (species, dose) has been carefully controlled for many years. Producers can only be expected to show prudence in the use of these compounds by using them in accordance with their official approvals. For those of us outside the regulatory system it would appear that if imprudence there be in this area, it lies within the actions of governments and regulatory authorities. For many years these products have been approved on a basic understanding which was restated as the only formal recommendation on the subject by the WHO meeting on antimicrobial resistance held in Berlin in 1997:
"The use of any antimicrobial growth promotion in animals should be terminated if it is: used in human medicine; or known to select for cross-resistance to antimicrobials used in human medicine"(1)
However, this approach has been 'mutated' over the past year to include all products which themselves, or whose related products, might possibly someday be used in human medicine. This in effect amounts to a "back-door" blanket ban on all such use. The so-called "precautionary principle" has been used as the justification, given that current EU legislation does not allow for a blanket ban. Since these products have been in use for 20-40 years it is highly questionable whether any human health benefit will be achieved by a "retrospective precaution" such as this. The application of a precaution which is not, itself, zero-risk, should only occur after a careful analysis of the risks of the various options available. The application of a blanket ban on these products based on limited experience in a few countries, which are not typical of the rest of Europe, could have a number of unintended consequences.
Swedish producers themselves acknowledge that they would not have been able to do without these products had they not previously instituted radical changes in their production systems to attempt to eradicate Salmonella infections (3). To force the rest of Europe rapidly down this route is likely to place European producers at a substantial disadvantage in competition with foreign producers not similarly burdened. This will lead to further reduced profitability of European agriculture with its inevitable effects on the ability to make the investments required to improve food safety and animal welfare. Increased imports from third countries will tend to reduce the European consumers influence on, and control of, issues such as animal welfare, food hygiene , residues. Because these products do not leave residues it will be difficult to enforce any ban on imports even if WTO rules allowed it. Concerns have also been expressed by veterinarians about indirect effects of product suspensions on the environment, animal welfare, animal disease and the need to use therapeutic medication (4,5,7). The issuing of "Guidelines on application of precautionary principle" issued by the EU Commission Consumer Affairs DG XXIV in October 1998 is to be welcomed (2). The final approved guidelines which will be used by both DGVI and DGXXIV are urgently needed. We await with interest, evidence of their application to the review of digestive enhancing antibiotics. It is widely accepted that antibiotics should be used prudently with a view to maximising their benefit and minimising risk to man. Suspensions/bans are acceptable where there is reasonable scientific evidence. However the balance of risk must be evaluated and be clearly favourable before a ban is introduced.
The RUMA Alliance
1. To review the use of antimicrobials in agriculture and to produce responsible use guidance for farmers.
2. To establish and communicate practical strategies by which use of antimicrobials might be reduced.
3. Ultimately to enable poultry producers to discontinue routine antimicrobial use without adversely affecting either the welfare of their animals or the viability of their business.
It is expected that the first papers arising from this process will be published shortly.
2. Belveze, H. (1998) Guidelines on the application of the precautionary principle.European Commission DG XXIV Consumer Policy and Consumer Health Protection 17th October 1998
3. Lundstrom, L (1999) Managing without Growth promotors. South West Broiler Conference, Cannington, Somerset February 10th 1999
4. Sainsbury, D.W.B. (1999) EU Ban on four antibiotic feed additives Veterinary Record 144(3)80
5. Taylor, D.J.(1999) EU Ban on four antibiotic growth promoters Veterinary Record 144(5)126
6. Thorp, B. McMullin, P.F. (1998) Antimicrobials Guidelines and "Mass Medication" Veterinary Record 143 (7):203
7. Thorp, B., Cargill, P. (1999) Ban of digestive enhancers. Veterinary Record 144(1)27-28