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RESPONSIBLE USE OF ANTIMICROBIALS IN POULTRY PRODUCTION

CONTENTS

Background

A. Antimicrobials in poultry production

6. Therapeutic antimicrobial products are used by veterinary surgeons in the treatment and control of many types of infection in a wide variety of animal species, including farmed poultry. If a number of animals in a group show signs of disease, both sick and healthy animals may need to be treated with therapeutic levels of an antimicrobial product for the recommended period. This is intended to cure the clinically affected animals, reduce the spread of disease and prevent clinical signs appearing in the remainder.

7. Antimicrobial substances used for digestive enhancement are administered in small amounts in the feed. Their use has been carefully controlled in the UK for over 30 years, and the principles laid down by the Swann Committee Report of 1969 have now been incorporated in to European regulations. These products are used in livestock production with a view to improving the efficiency of digestion of animal feeds. In addition they have important environmental benefits.

8. There is a large body of scientific literature on the use of antimicrobials of different types in poultry. Much of this has been generated by pharmaceutical companies as part of the process of developing new products and achieving their approval by the UK regulatory body, the Veterinary Medicines Directorate, on the basis of safety, quality and efficacy. Antimicrobial use in many other poultry producing (and exporting) countries is much more widespread and less well controlled than in the UK.

9. Table 1 below lists diseases of poultry most commonly requiring medication. While some of these diseases are not caused by bacteria (e.g. coccidiosis and blackhead) the medicines used commonly do have some antimicrobial activity.

10. Antimicrobials which are authorised for use in poultry in the UK are detailed in the current editions of either the Veterinary Data Sheet Compendium, published by NOAH, and/or the Handbook of Feed Additives, published by HGM Publications. It must be emphasised that antimicrobial use is not regarded as the prime defence against disease and production losses. A wide range of management techniques (disinfection, eradication, isolation, competitive exclusion) and vaccines are routinely used which prevent or reduce the need for antimicrobials. Some companies have adopted a policy of not using antimicrobials prophylactically without a well-defined indication. We can summarise the fields of antimicrobial use as follows:

11. Treatment of clinical disease
Coli-septicaemia, either acute or sub-acute, is a common sequel to a number of viral diseases of poultry, especially those caused by viruses of the respiratory system. Many of the products listed as "solubles" in the Compendium will be appropriate for this indication. While the sub-group fluoroquinolones are indicated broadly for the treatment of pasteurellosis, mycoplasmosis and colisepticaemia, in practice their use is limited to high-value or very young stock or unusually severe disease because of their high cost compared to other antimicrobials.

12. Salmonella in poultry in the UK does not usually require medication. Specific Salmonella serotypes with a special tendency to develop antimicrobial resistance (i.e. S.typhimurium DT104) clearly need special control measures, and treatment decisions relating to other diseases need to take into account incidental exposure of such organisms to medication. In particular it is vital that accurate information on changing patterns of antimicrobial susceptibility in pathogens monitored under government programmes is rapidly made available to those prescribing the products so that appropriate changes in control measures are made. Samples of ill or dead birds are routinely subjected to PM examination to confirm the diagnosis and, commonly, to isolate and sensitivity-test the pathogen.

13. Prevention of clinical and sub-clinical disease
Some bacterial infections are best dealt with by treatment before the clinical signs. Many such infections have been eliminated from the majority of the poultry population by means of eradication (e.g. Mycoplasma gallisepticum, M. meleagridis, M. synoviae). However there is a reservoir of these infections in "back-yard" flocks, game birds and, possibly, wild birds. "Breaks" can be expected, and, in this circumstance it will be common to treat the affected parent flock and the progeny with an appropriate product.

14. Programmes will vary widely according to the particular infection, the pathogenicity of the strain, the types of problems encountered and intercurrent infections. Some years ago it was common for all starter feed to be medicated up to 10-20 days of age with a view to controlling non-specific infections. This is now much less common. Where routine medication is used it is more likely to be short term (3-5 days) in drinking water, and may be targeted at particular "at-risk" populations (such as the progeny of very young or old parent flocks).

15. Modification of intestinal bacterial flora
Digestive enhancing or "Growth Promoting" antimicrobials are routinely used in most poultry-producing countries to moderate the balance of intestinal bacteria. It has been estimated that intestinal bacteria may utilise up to 10% of the energy in a typical diet. Their main effect is not really to enhance growth (commercial broilers rarely are grown anywhere close to their genetic potential), rather to improve production efficiency by better feed conversion - hence the more accurate term "Digestive Enhancer".

16. A significant benefit for animal welfare results from the improvement in the utilisation of nutrients and the reduction in the volume or moisture of undigested material deposited in the animal's environment. There are also beneficial effects for the overall environment with reduced feed meaning fewer lorry journeys, lower water use and reduced arable land required to be planted in cereals.

17. In addition to their direct economic effects, digestive enhancers also have benefits in the control of sub-clinical and clinical disease. This group of products can play a role in controlling the adverse effects of non-specific enteritis (of nutritional or viral origin) and in reducing the risk of necrotic enteritis and cholangiohepatitis.

18. To address medical and public concerns about the use of these compounds FEFANA (the European Federation of Feed Additive Manufacturers) is currently (1998-2001) funding a detailed survey on resistance patterns in intestinal bacteria from the major food species in a number of European countries. It is to be expected that the results of this information and various other research initiatives in this area will provide sufficient information to develop a proper risk assessment of this issue.

19. Anticoccidials
Ionophore anticoccidials are not used specifically for the control of bacterial infections. They have, however, an important, though narrow-spectrum, efficacy against some intestinal bacteria, and could therefore affect bacterial sensitivity. Their use is vital for the prevention of severe suffering and economic losses (clinical coccidiosis will occur in untreated chickens). It must be understood that other anticoccidials have no anti-bacterial effects, and it is necessary to have and use these other products in order to conserve the efficacy of the ionophores. For this reason ionophore anticoccidials cannot be seen as a replacement for antimicrobial digestive enhancers.

25. Farmer responsibilities
It is the responsibility of the farmer to clearly give their veterinary surgeon responsibility for the health of the animals and to co-operate in ensuring that such responsibility is real.

Specifically, the farmer should:

a. Regard therapeutic antimicrobial products as complementing good management, vaccination, and site hygiene.

b. Initiate medication only with formal veterinary approval, provided either by a prescription, a verbal direction or an approved treatment programme or protocol. In the case of in-feed medication, this will be provided by a "Medicated Feedingstuff Prescription" or MFSP prescription.

c. Ensure that accurate information is given to the veterinary surgeon in order that the correct dosage can be calculated for the birds concerned, and ensure that clear instructions for dosage and administration are obtained and passed on where necessary to the staff responsible.

d. Always complete the course of treatment at the correct dosage. Ensure that the dosage is consumed in an effective manner by careful administration.

e. Accurately record the identity of the animals medicated, the batch number, amount and expiry of the medicine used, the withdrawal period required and the date and time the medication was completed.

f. For in-feed or in-water medication ensure that the end of medication is accurately determined by cleaning the header tank or feed bin as appropriate.

g. Keep on file information on any medicines used, for example, the package insert, product data sheet, or the safety data sheet as appropriate.

h. Report to their veterinary surgeon any suspicion of an adverse reaction to the medicine in either the treated animals or farm staff having contact with the medicine. This should include any unusual failure to respond to medication. Such reports may also, if desired, be made directly to the Veterinary Medicines Directorate at Woodham Lane, New Haw, Addlestone, Surrey KT15 3BR. Copies of a poultry-specific "green form" are available for this purpose. A record of the adverse reaction should also be kept on the farm.

i. Ensure that the appropriate withdrawal period is complied with prior to the sale or collection of the treated birds or eggs for human consumption. In general the withdrawal time required is specified on the MFSP or prescription. Note that if in the professional judgement of the veterinary surgeon, it is necessary for a product to be prescribed for a species for which it is not licensed or at a dosage higher than the licensed dosage, then an appropriate withdrawal period should be specified to ensure that food produced from the treated animals does not contain residues harmful to consumers. In general this should be not less than the following:
Eggs 7 days
Meat from poultry 28 days

j. Co-operate with QA schemes which monitor antimicrobial usage, medication documentation, and withdrawal period compliance. However such schemes should not constrain the attending veterinary surgeon from preventing suffering in the animals under their care.

k. Track antimicrobial usage taking account of the potency of various products. The simplest approach is to record the number of kgs. of animal treated/day as a proportion of the total kgs. of animal at risk for each species and class of stock. Any usage where the mg/kg dosage does not match licensed values would need to be highlighted.

l. Ensure that different medicines are only given at the same time when this is with the specific approval of the veterinary surgeon because adverse interactions sometimes occur.

m. Maintain a medicine log book on farm together with copies of relevant regulations and Codes of Practice.

B. Practical strategies for reducing the need for antimicrobials

C. Enabling poultry producers to discontinue routine antimicrobial use without adversely affecting either the welfare of their animals of the viability of their business.

Appendix A.

Ways to reduce the need for antimicrobial treatment

A1 Introduction
The scientific definition of health in an animal is the "absence of disease". In commercial poultry production this would normally be extended to include freedom from infection of certain potentially pathogenic bacteria and zoonotic organisms. Bacteria-free chickens in isolation under laboratory conditions grow approximately 15% faster than similar chickens in a "conventional" environment. This ideal is economically impossible to achieve under practical farm conditions. The use of immunisation, sanitation, preventive medicine and biosecurity are recommended as the major and primary preventatives for infectious disease. Medication for prevention or treatment is only to be recommended when the other measures are not feasible or are ineffective.

A2 Stockmanship and environment
Probably the single greatest factor impacting on health status of farmed livestock is stockmanship. Some of its effects will be through implementation of the various other measures discussed below. Some will be through adaptation of the management regime (feed, lighting, litter, ventilation, temperature control, humidification) in response to subtle changes in flock well-being. Improved environmental control systems which dampen variations due to season, weather and diurnal variation can also have a positive impact. Mechanical and electronic systems of environmental control need to be routinely checked. Computerised systems should be seen as an adjunct to the good stockman, not a replacement.

A3 High health status stock
Every poultry flock begins as a delivery of day-old birds. The health status on delivery has a very large impact on future health and performance. A formal health specification should be agreed with the supplier. This may include the following categories:

a. Freedom from specified pathogenic Mycoplasma infections such as M.gallisepticum, M.synoviae, and M.meleagridis (turkeys only).
b. Freedom from specified or all Salmonella serotypes
c. Produced from flocks immunised or antibody positive for specified vertically transmitted infections (such as Avian Encephalomyelitis and Chick Anaemia Virus)
d. Produced from flocks immunised to provide passive protection (see below) for specified infections that the birds are likely to encounter (e.g. Infectious Bursal or Gumboro Disease).
e. Immunised at the hatchery using effective and well monitored procedures ( e.g. for Marek's disease or Infectious Bronchitis).

f. Incubated, hatched and transported under optimal environmental conditions for the species, size of egg and age of parent flock.
g. Incubated, hatched and transported under sanitary conditions as monitored by a routine sanitation-monitoring programme.

A4 Having listed the above it must be recognised that the day-old chick/poult/duckling is not and can never be absolutely uniform. Biological variability exists, not least according to the age of the parent flock. Effective communication and co-operation between the hatchery and farm can do much to minimise the health effects of such variation.

A5 Production planning and system organisation
Poultry production is among the most complex of agricultural production systems. Its multi-stage nature (grandparent flock, hatchery, parent flock, hatchery, commercial bird, product), combined with a very short "shelf life" of intermediate products (hatching eggs, chicks), means that production planning can have an enormous impact, both for good and for bad, on the health status of a production system. Wherever possible all-in-all-out production should be planned on a site basis. The time required for effective cleaning and disinfection between flocks will depend on many factors such as the type of equipment, surface finish, state of repair and so on. Whatever the planned "turn-around", compliance with the plan should be monitored over time.

A6 Cleaning and disinfecting houses and equipment
When poultry are removed from houses, the buildings and equipment should be
carefully cleaned and disinfected before new birds are introduced. Manure (including litter) should be removed from the immediate vicinity of the poultry houses, preferably to an off-site location. A successful cleaning and disinfection protocol should:
a. Plan to include site specific issues such as required maintenance
b. Remove birds, check rodent bait
c. Remove mobile equipment
d. Remove litter and as much other material as possible
e. Wash to remove maximum organic material
f. Clean/sanitise water system
g. Clean/sanitise all surfaces - record concentration and usage
h. Clean/sanitise equipment
i. Setup equipment
j. Fog

A7 The appropriate detergents and disinfectants will vary with the nature of the production system and disease or infection challenge. In all cases, however, effective cleaning, and careful identification and separation of unsanitised and sanitised areas/materials will maximise the efficacy. Always use MAFF approved products.

A8 Careful attention should be given to feed bins, watering devices and water lines to be sure that these are free of disease agents. Water lines should be flushed and then a disinfectant solution pumped into the lines. These lines should be closed and allowed to rest for at least 24 hours, and then thoroughly flushed to remove the disinfectant.

A9 Site and house biosecurity
Biosecurity is the utilisation of methods which stop the transfer of infection into or between components of production systems. Major components include:

a. allow only necessary visitors to production sites - most sites will have a "quarantine period" applied to visitors with access to sites in other production systems, typically of 3-7 days.
b. restrict movement of workers and equipment between houses, sites and age groups. Here too it may be necessary to implement quarantine.
c. provide sanitising foot baths, showers and protective clothing at strategic locations;
d. maintain cleaning and disinfection programs, especially in hatcheries;
e. reduce microbial load on vehicles and other mobile equipment by washing and disinfecting at critical times;
f. locate production sites strategically in relation to other production sites and movement of poultry, thus minimising transfer of disease;
g. restrict contact of workers with other poultry, especially potential carriers of hazardous disease organisms;
h. appropriately handle waste and dead birds to minimise the transfer of disease between sites;
i. control rodents and wild birds effectively, since both are potential disease vectors.

A10 Competitive exclusion
Day old chicks have a much simpler gut flora (i.e. fewer bacterial species) than the adult bird. Competitive exclusion seeks to establish a complex "normal" gut flora in the chick with the aim of decreasing the opportunities for particular pathogens to colonise the intestine and the caecum. There is a question as to how competitive exclusion products should be categorised, and currently no competitive exclusion products are licensed as medicines in the UK. Nevertheless, in the UK these products are quality controlled and have been widely used without reported adverse effects.

A11 Antimicrobials treatments to control disease will tend to have the side effect of simplifying the "normal flora". Use of a broad-spectrum competitive exclusion product is a way of balancing this process. The bacteria present in these preparations should have acceptable sensitivity profiles. Their use could, theoretically, help restore sensitive bacterial populations in a flock treated with antimicrobials, or on a farm after removal of a treated flock. If they contain commensal E.coli strains (of low pathogenicity), or other bacteria which compete with pathogenic E.coli, they may have a side effect of reducing the need for antimicrobial treatment of coli-septicaemia.

A12 Nutrition
Today's modern poultry breeds have a phenomenal potential to eat feed and produce meat at very reasonable cost. A combination of improved genetics and better feed has produced a highly efficient bird. Nutrition of the modern bird is a very complex area and it is best to heed the advice of the nutritionist and feed compounder to produce feed with an appropriate balance of nutrients. The nutritional specification must be married with a suitable feeding programme to supply the growing bird with its daily nutrient requirement.

A13 The two major nutrients which lead to fast growth rates are protein and energy. The balance of amino acids in the protein is used for meat production following digestion. Energy, derived mainly from fats and carbohydrates in the feed, fuels the process of growth. The correct mineral balance ensures good skeletal development, more important as the broiler is maturing earlier. Appropriate vitamin levels prevent deficiency problems and stimulate the immune system.

A14 The raw materials used in broiler diets must be of wholesome quality. The feedmill will have a programme of testing to ensure that inferior quality materials are avoided and that the finished feeds meet the nutritional targets required. Choice of an appropriate anticoccidial programme is essential to control the coccidiosis challenge. Anticoccidial use should be reviewed regularly to avoid resistance buildup. The feed compounder can use their expertise to combine the raw materials available in the most cost-effective way giving feeds of high nutritional value to grow the modern bird efficiently.

A15 Feed hygiene
The protection of human and animal health must always be a prime consideration in the manufacture and distribution of animal feedingstuffs. Feed mills must have a comprehensive and documented system for the production of safe animal feedingstuffs with the requirements of the UKASTA Code of Practice for the Manufacture of Safe Compound Animal Feedingstuffs, or a proven equivalent. These requirements include a rigorous HACCP procedure and adherence to the MAFF/DANI Codes of Practice for the control of Salmonella.
a. raw materials
Feed materials should be sourced with a view to minimising contamination with poultry and zoonotic pathogens. The origin, transport, storage, processing and handling of feed material must be considered. Store hygiene is particularly important and should be verified by annual inspection or membership of a recognised Assurance Scheme.

b. Although some feed materials are processed prior to arrival at the feed mill, the majority of feed material will be unprocessed and direct from the farm or intermediate storage. Feed raw materials may be processed to improve the nutritional quality of the material or to reduce undesirable bacteria, such as salmonella. Some materials will have been exposed to high temperatures, for example, temperatures of 80oC or more for varying periods of time. The decontaminating effect will be reduced if there is contamination between treated and untreated materials. Any material known to be contaminated with salmonella should be put through a heat or chemical treatment to destroy the micro-organisms before the material is used for animal feedingstuffs.

c. finished feed
Finished feed may undergo a final decontamination either through a high temperature process or through the use of chemicals such as organic acids. Where they are applied, the principle of separation of treated from untreated feed materials must be applied in order to ensure no possible re-infestation. This can be obtained by limiting personnel access, filtering air to coolers and generally ensuring that finished products are kept well clear of incoming feed material and any air which might contain dust from these materials. Cooling equipment is especially important given the range of temperatures which exist within them (some of which may allow bacterial or mould growth) and their high demand for air.

d. transport and delivery
Feed materials or compound feedingstuffs may be readily contaminated if placed in contaminated vehicles. Vehicles used for carrying feed materials and finished feedingstuffs must comply with the UKASTA Code of Practice for Road Haulage and the UKASTA Feed Assurance Scheme or proven equivalent. Particular attention must be paid to vehicle hygiene and cleanliness, correct loading, avoidance of contamination and cross-contamination and delivery to correct farm facilities so that the feedingstuff is received by the correct livestock.

e. Vehicles may be contaminated from the general environment (e.g. road
spray), farm environment (when loading or unloading), or from the
transport of raw materials ("backloading"). These risks need to be
evaluated for the specific feed production system, and they need to be
managed with a balanced approach to vehicle dedication, maintenance and cleaning. Vehicle drivers must not enter poultry houses. Where possible, feed should be transferred to bins on site without vehicles having to go within the biosecure area.

f. farm storage
Bins can harbour a range of bacteria, moulds and even coccidial oocysts. Bin hygiene may be substantially influenced by the design of the installation to reduce air and dust contamination within the house. Condensation (relating to temperature of delivered feed), and poor weather proofing will also strongly influence conditions for microbial growth in the bins. It should be kept in mind that conditions may support the growth of organisms which have direct relevance to bird or human health (E.coli and Salmonella respectively). Also mould growth may result in production of mycotoxins which, even if they do not cause typical disease, can have a substantial effect on productivity. Smooth bin surfaces and access for inspection and, if required cleaning, are especially critical at farm-depletion to ensure that bins and augurs are not a source of contaminated material for the next flock.

g. treatments
A number of products, mainly based on mixtures of organic acids and their salts, are commonly used to reduce bacterial numbers and prevent their growth in feed. Complete decontamination of feed using these products alone is difficult. However many of these will continue to act for some time after their application and can, potentially, improve the general hygiene of the feeding system right the way through to the bird feeder. They should not be regarded as a substitute for the hygienic measures noted in the previous sections.

A16 Drinking water hygiene
Drinking water is the largest single input into any poultry production system. It should be potable i.e. of a quality suitable for human consumption. However this alone is not enough. The importance of effective cleaning and sanitising of drinker systems at farm depletion has been emphasised. Nipple drinkers are the preferred type. Particular drinker systems (e.g. "bell type") are, by their nature, prone to bacterial contamination from the air. All drinker systems are prone to microbial growth when exposed to high environmental temperatures and low flow. These conditions apply especially during the first 1-3 weeks of life of young poultry.

A17 Even if chlorinated public water supplies are used, the residual chlorine will
be insufficient to control the risk of contamination. Dosing with approved water sanitisers during the first few weeks, during periods of disease challenge, or even throughout the life of some classes of poultry will help minimise this risk. Care must be taken with dosage to ensure effective doses without reducing water intake. If using chlorine-based treatments, residual levels of 1-5ppm at drinker level have been recommended (Herrick, 1974). Simple colorimetric test kits are available to estimate residual chlorine levels. This is necessary as the amount of chlorine required will be affected by the physical nature of pipework and the degree of accumulation of bio-film or other organic matter on surfaces.

A18 Mild acidification of water lines may be used as an alternative to chlorination (it should certainly not be done at the same time). This is especially useful for cleaning water systems prior to the use of medication or vaccination. It is vital that no water treatments should interfere with vaccines applied in drinking water. Consult your poultry veterinary surgeon and/or vaccine manufacturer for specific advice in this area.

A19 Litter
In deep litter systems, any litter introduced, whether at the beginning of the flock or in re-littering, is a potential source of contamination with disease-producing organisms. In general terms wood shavings are less likely to present a bacteriology hazard than untreated straw. Contamination with spores of mould (usually Aspergillus fumigatus) can cause disease in young chickens, and turkeys of any age. It occurs when litter materials have been high in moisture content and exposed to warm temperatures. Even if temperatures subsequently drop and the material dries out, large numbers of spores will persist.

A20 If litter is to undergo a treatment process then similar concerns about separating treated and untreated material apply as for feed and raw materials (see section A15 above). Finally the process of storage, transport and delivery of litter into the poultry house should be reviewed with a view to avoiding re-contamination. The weakest link in this chain is likely to be the actual delivery of litter into the poultry house. The external environment of the farm is likely to have some contamination from the previous flock when this is taking place.

A21 Immunisation
Vaccination against primary viral pathogens helps reduce the need for all types of antimicrobial medication. Facilitation of the licensing of a broad range of cost-effective vaccines, which are safe and effective under field conditions, is the measure open to the regulatory authorities which is most likely to reduce the need for therapeutic antimicrobials, and, hence the risk of resistance development.

A22 The deliberate induction of immunity by vaccination is far more preferable than natural induction following unpredictable exposure to field infection. Numerous infections, sometimes in combination, can kill or debilitate susceptible poultry causing pain and suffering in addition to losses in performance. Immunity is of two broad types: passive or active.

A23 Passive immunity occurs as antibody in the yolk of developing embryos and derives from the maternal bloodstream and is present until metabolised (for 2-4 weeks) in the blood of newly hatched chicks. Passive immunity is generally effective against viral diseases, but less so or ineffective against bacterial infections, e.g., mycoplasmas or salmonellae.

A24 Active immunity occurs when an antigen is introduced to the bird and processed through the bird's immune system, resulting in various protective responses which will act to protect the bird if it is re-exposed to that antigen. Active immunity can be produced either by living or inactivated antigens, or a combination of the two. Live vaccines can be administered either to individual birds, such as by injection or eyedrop, or to large numbers of birds via the drinking water or by aerosol.

A25 Inactivated vaccines must be given by injection. These usually incorporate potent adjuvants which enhance the local cellular reaction and, therefore, increase the immune response.

A26 Immunity against some infections can be induced by injection of vaccine into the egg shortly before hatching, so that active resistance is developing before any exposure can take place.

A27 Development of immunisation programmes
The development of an immunisation programme should be based on knowledge of the diseases to which birds are likely to be exposed and incorporated into the management system of the flock. It requires knowledge of the presence and level of passive immunity so that immunisation can be properly timed. Timing is also important so that vaccines do not detract from each other's responses or exacerbate their clinical effects.

A28 Vaccines should not be administered when other stressors are acting on the flock. Immunisation cannot be a substitute for proper sanitation and biosecurity and programmes cannot totally protect birds which are stressed or in unhygienic conditions. Vaccines should be purchased and utilised only after full consultation with a poultry veterinary surgeon. Where monitoring tests are available, e.g., serology, these should be routinely utilised to ensure that vaccine responses have taken place.

A29 Dead bird disposal
Successful methods of dead bird disposal must prevent spread of pathogens to
surviving birds, contamination of surface or ground water, and risk to human health. Several methods are acceptable in commercial systems. Strict biosecurity rules need to be applied to any system involving routine collections of dead birds from different sites. This is usually achieved by having a dead bird collection point outside the biosecure zone.

A30 Control of insects, rodents and exposure to wild birds
Rodents, insects and wild birds can harbour many pathogens which will cause disease and infections in poultry. An integrated system of control of the numbers of these organisms (where legally permitted) and limiting contact between them and poultry (where possible) is advised. Monitoring systems should be used to ensure that action is taken in the early stages of a population rise rather than afterwards is key to the success of these programmes. They are particularly important during farm depletion.

A31 Veterinary health plan programming
The previous sections illustrate the multi-faceted nature of disease control measures which are available. The relative importance of each measure, and the way in which it should be applied will vary from company to company, and, to a lesser extent, from farm to farm. The various measures can interact in complex and, sometimes, unexpected, ways. Requirements will also tend to evolve over time and be affected by seasonal influences. Detailed preventative medicine programmes should be documented. These should include all routine medications (including non-prescription medicines such as anticoccidials, digestive enhancers, anthelmintics), competitive exclusion and probiotic treatments and vaccines.

A32 Any prescribing of antimicrobial medication should take into account its possible effects on other aspects of the programme. The programme should also include all routine samplings for infection, disease and/or response to vaccination monitoring. It should be used in conjunction with an agreed protocol of actions with respect to circumstances in which further samples (e.g. post-mortem submissions) are required. Routine examination of a sample of daily mortality or culled birds is recommended in many circumstances.

A33 The use of therapeutic antimicrobial products in the absence of clinical disease or specific pathogenic infections and, in particular, long-term administration to prevent disease should not be practised without a clear justification. Prophylactic medication may be appropriate in certain precisely defined circumstances. Each company or farm should work with its veterinary surgeon to develop a written policy or protocol covering the circumstances in which this is appropriate.

A34 Programme monitoring and auditing
A health programme on paper achieves nothing. It must be translated into practical actions which are documented, and audited, and any corrective measures implemented.

A35 Sensitivity monitoring and tracking
In an outbreak of disease, the sensitivity of the causal organism should ideally be ascertained before therapy is started. In disease outbreaks involving high mortality or where there are signs of rapid spread of disease among contact animals, treatment may be started on the direction of the veterinary surgeon on the basis of clinical diagnosis. Even so, the sensitivity of the suspected causal organism should, where possible, be determined so that if treatment fails it can be changed in the light of the results of sensitivity testing. Antimicrobial sensitivity trends should be monitored over time and such monitoring may be used to guide clinical judgement on antimicrobial usage.