biosecurity: reducing disease risks to pig breeding herds · pig producers have probably suffered...

In Practice ● MA Y 2005230

DISEASE RISKS AND SOURCES OF INFECTION

Diseases exhibit a broad spectrum of infectivity and farmsvary widely in their ability to institute preventive mea-sures. Hence, each unit needs to be evaluated individuallywith particular reference to herd location, preventablerisks and financial constraints. Procedures need to be

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DISEASE imposes considerable constraints on the productivity and profitability of the livestock industry.Pig producers have probably suffered more than other sectors from the devastating effects of asuccession of infectious disease outbreaks over the past 30 years. Many of these have been highlycontagious viral diseases, including transmissible gastroenteritis (TGE), swine influenza (SI), Aujeszky’sdisease (AD), and porcine respiratory and reproductive syndrome (PRRS). Postweaning multisystemicwasting syndrome (PMWS), which is linked to porcine circovirus (PCV-2) infection, has challenged the very survival of the pig industry in Britain and elsewhere. Even long established endemic diseases, suchas enzootic pneumonia (EP) and swine dysentery (SD), still cause significant losses if introduced into naiveherds. The recent reappearances of classical swine fever (CSF) and foot-and-mouth disease (FMD) inBritain were timely reminders that there is no place for complacency in disease prevention programmesat both national and herd level. The concept of biosecurity, which gained prominence in Britain duringthe FMD epidemic, encompasses the full range of measures aimed at disease prevention. In fact, it is oneof the cornerstones of the Government’s Animal Health and Welfare Strategy for Great Britain, whichaims to promote biosecurity to a livestock industry that, in the past, has not always given it high priority.This article reviews the most important sources of disease on pig units – and, thus, the key areas forconsideration in terms of farm biosecurity.

Biosecurity: reducing disease risks

to pig breeding herds

GEOFF PRITCHARD, IAN DENNIS AND JAKE WADDILOVE

Zero disease risk on farms isunachievable and no biosecuritysystem is perfect. However, whilebreakdowns will inevitably occur,particularly in pig-dense areas,adherence to sound basic biosecurityprinciples will reduce risks to aminimum

Geoff Pritchardgraduated fromEdinburgh in 1973. He has worked for the VeterinaryLaboratories Agencysince 1980 and is basedin Bury St Edmunds,Suffolk. He holds an FRCVS for studies on the epidemiologyof transmissiblegastroenteritis in pigs.

Ian Dennis graduatedfrom Bristol in 1977.After working inmainly cattle practicein Devon for twoyears, he moved toEast Anglia where heis a partner in a mixedpractice. He holds theRCVS certificate in pigmedicine.

Jake Waddilovegraduated fromCambridge in 1978. Heis a principal partner in a practice in Bury St Edmunds where he works almostexclusively with pigs.

In Practice (2005)27, 230-237

Principal considerations for farm biosecurity

■ Live pigs – Contacts– New stock (including semen and embryos)■ Local spread■ Herd location■ Vehicles (especially if transporting pigs or otherlivestock), equipment and consumables■ Humans (eg, visitors and farm staff)■ Feed, water and bedding■ Wildlife and vermin

Fomites

Infection present in faeces (the main source), saliva,nasal secretions, blood, milk or semen may bemechanically transmitted between animals on avariety of different inanimate objects – or fomites.These include contaminated clothing, boots, vehi-cles, equipment, bedding and feed.

The period of time that fomites remain infec-tious depends on the nature of the agent and envi-ronmental factors such as temperature, exposure toultraviolet light and the efficacy of disinfection pro-cedures (see box on page 233). Porcine parvovirus(PPV) and PCV-2, for example, are very resistant andsurvive well for several months under common UKenvironmental conditions. Brachyspira hyodysente-riae – the cause of swine dysentery – is reported tosurvive in moist faeces for up to 40 days. PRRS virushas been isolated from trailers which have beencleaned and disinfected and rested overnight incold conditions without drying; there are otherrecorded examples of PRRS virus surviving in theenvironment for several weeks in buildings.

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In Practice ● MA Y 2005 231

heightened during notifiable disease alerts. The HazardAnalysis Critical Control Point (HACCP) system, intro-duced originally for the food industry, offers some usefulprinciples that can be adapted for use on farm to deal withdisease risks. This identifies hazards, establishes criticallimits and introduces monitoring and recording systems to deal with the risks. The principal considerations withrespect to biosecurity on pig farms are listed in the left-hand box on page 230, and are discussed, in turn, below.

LIVE PIGS

Direct contact with other live pigs (including feral wildboars) presents the main specific risk for acquiring newinfections. Pigs may be clinically affected, apparentlynormal but incubating disease, convalescent carriers orlong-term excreters of pathogens. The likelihood of dis-ease transmission is exacerbated by stress due to loading,mixing and transportation. Semen and embryos also present a risk in relation to viral diseases such as PRRSand CSF (as illustrated by recent experiences in theNetherlands).

Most herds buy in breeding replacements for geneticimprovement. It is important that these animals aresourced appropriately and health-matched with the recip-ient herd, and undergo a period of isolation (see boxbelow). Health status is essentially an assessment of herdimmunity and current disease activity. Ideally, incomingreplacements should be of similar or higher health statusthan the recipient herd to prevent them from introducinginfections not already present in the recipient herd.Conversely, if they are inappropriately ‘disease free’ and

Transmissible gastroenteritis is a highly contagious diseaseof pigs that was prevalent in the 1970s and 1980s, but isnow apparently absent from Britain

Postweaning multisystemic wasting syndrome was firstconfirmed in Britain in 1999 and remains a very seriousdisease problem for the pig industry

Isolation of incoming animals

Irrespective of how reliable the health status of the herd of origin is, it is impor-tant that incoming gilts or boars undergo a period of isolation (or quarantine)for at least three to four weeks. The duration will depend on the particular diseases of concern (eg, eight weeks for EP). The feasibility of adopting a worth-while isolation period is improved by reducing the number of intakes and bring-ing gilts in at a younger age (eg, 30 to 100 kg in one batch). Isolation allows pigsto recover from the stress of a journey and adapt to a new environment, and anyincubating infections to become evident in a contained environment. This shouldbe followed by gradual acclimatisation and challenge with resident pathogens,ultimately leading to full integration into the herd, ideally combined with theuse of sentinel pigs. In the USA, it is commonplace to follow 60 to 90 days of iso-lation with a 30-day ‘cooling-off’ period. At present, in Britain, the majority ofherds – to their cost – do not routinely isolate replacements.

Isolation provides an opportunity for clinical inspection, laboratory testingand vaccination, if appropriate. For example, examinations for sarcoptic mange,tests for Salmonella infection or serology for diseases such as PRRS could beundertaken. Laboratory techniques are constantly being upgraded, particularlywith the rapid advances in biotechnology and the introduction of new PCR testsand ELISAs. Veterinary surgeons should check with the laboratory to which sam-ples are to be sent to establish which tests best meet current requirements.

Guidelines for isolation units■ Ensure that biosecurity of an isolation unit is at least as good as that of the main herd■ Locate isolation units at least 50 m from the main herd, preferably onanother site■ Consider the risks from effluent and drainage outputs ■ Ensure that buildings are easy to clean and disinfect■ Provide clean dry bedding and readily available water■ Ensure good lighting and accessibility of animals for visual inspection■ Use dedicated boots and clothing (and, ideally, personnel) ■ Isolate animals for at least three to four weeks ■ Make regular clinical inspections and observe animals closely ■ Operate isolation premises on an all-in, all-out basis

Guidelines for obtaining breedingreplacements

■ Know the disease status of both the recipientand source herds■ Consider the location of both herds and endemicdisease risks■ Acknowledge the limitations of recipient herd biosecurity■ Select an appropriate single source for replacements■ Seek both genetic improvement and sound disease control■ Assess the biosecurity status of the breedingpyramid■ Consult with the breeding company’s veterinary surgeon■ Check company claims, monitoring records andback-up service■ Confirm that there has been no recent diseaseoutbreak on the farm of origin■ Check what diseases have not been tested for■ Ensure a continuous supply of pigs of appropriate status



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immunologically naive to common infections, they mayneed protecting by vaccination or acclimatisation beforeentering the new herd. This also applies if a new herd islikely to suffer a disease breakdown because of location(see later).

Replacement profiling requires knowledge of the dis-ease status of the herd of origin and the recipient herd.Disease status information can be obtained from varioussources, including records of clinical disease history,performance records, serological monitoring, necropsyfindings, lung/snout scores and other abattoir reports. Anenhanced abattoir monitoring programme for the pigindustry in Britain (British Pig Health Scheme) has beendeveloped by the British Pig Executive (BPEX) and isdue to be launched in July 2005. Its recently introducedZoonoses Action Plan (ZAP), based on meat juiceELISA testing at the abattoir, can indicate exposure toSalmonella species and gives a potentially useful guideto status although it mainly measures zoonotic risk ratherthan clinical disease. Most reputable breeding companieshave in-house health-recording programmes and thecompany veterinary surgeon will be responsible for liais-ing with the customer’s veterinary surgeon.

LOCAL SPREAD

The generic term ‘local spread’ is often used in areas of high local livestock density where it is impossible to determine precisely how an infectious agent enters aherd. Unexplained disease transmission over short dis-tances is often attributed to aerosol infection, but it isvery difficult to exclude the possibility of local spread by other routes, particularly wildlife. Aerosol spreadappears to occur to a variable extent with a number ofdiseases including EP, PRRS and PMWS; long distanceairborne spread in viral plumes is well recognised withFMD and AD. Aerosol and airborne spread depend on

Pig units should be sited away from potential sources of infection such as landfill sites, abattoirs and other pig herds

Checklist of physical biosecurity measures

■ Remote location and single approach road (no public rights of way) ■ No nearby livestock farms, abattoirs, landfill sites, sewage works, and so on■ Clear farm identification ■ Farm office or reception area off-site ■ A bell or phone to attract attention ■ ‘Keep out’ warning signs■ Controlled access with single, well located farm entrance■ Strategically placed, well maintained disinfectant footbaths■ Off-site car park, with easily cleaned and disinfected hard standing ■ Well defined farm boundary and wildlife-proof perimeter fence■ Changing/showering facilities and separation of clean/dirty areas■ Good hand washing facilities for visitors and workers■ Dedicated farm equipment, protective clothing, boots and vehicles■ Loading/unloading bay for live pigs away from the main herd ■ Completely separate bay for carcase removal or on-farm incineration facilities■ Good separate isolation facilities for added stock ■ Feed bins sited on farm perimeter, with farm-dedicated ownblower pipes■ Bird- and vermin-proof buildings, as far as practicable■ Good facilities for slurry or manure collection and disposal■ Off-site lorry wash facilities with trained operatives■ ‘Don’t feed the pigs’ sign for outdoor herds

Demographics of the UK pig population showingconcentration in areas such as East Anglia and Humberside. Picture, British Pig Executive

Good, controlled access to a pig unit showing the farmoffice and security gates



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Disinfection procedures

The ideal disinfectant■ Proven broad-spectrum activity and efficacyunder farm conditions■ Fast acting to rapidly kill highly infectiousagents■ Temperature stable and active at extremes ofheat or cold■ Stable after dilution, especially for footbaths■ Suitable for porous and non-impervious surfaces■ Active in the presence of organic matter■ Versatile for use in footbaths, vehicles and surfaces■ Safe for environment, animals and operativestaff■ Government approved for notifiable diseases ■ Easy to store■ Cost effective

Disinfection is a targeted procedure aimed at reduc-ing disease transmission via contaminated protectiveclothing (particularly boots), vehicles or equipment.It is an important line of defence in good biosecuritypractice, but should be considered as an adjunctmeasure rather than a stand-alone procedure. Disin-fectants require the effective removal of organicmatter to be fully efficacious. It is essential to use thecorrect concentration (a minimum of DEFRA GeneralOrders rates). Adequate prior cleaning of buildingsand equipment should be carried out. These shouldbe allowed to dry after washing and disinfectantshould be applied to saturation point. Thoroughapplication, including the undersurfaces of equip-ment, should be ensured. Care should be taken notto recontaminate recently disinfected surfaces.

Too much reliance is often placed on disinfectantfootbaths, particularly in farm situations with basical-ly poor hygiene and scrapethrough slurry handlingsystems, which facilitate the spread of pathogens.Accumulating faecal matter, dilution by rainwater,incorrect concentration and infrequent replenish-

ment may render footbaths more a source of conta-mination than a means of preventing mechanicaltransmission of infectious agents. Merely standing inor walking through a disinfectant footbath with min-imal contact time does little more than lull staff intoa false sense of security.

However, if instituted properly at strategic loca-tions on the farm, footbathing is a very useful adjunctto other measures and also heightens awareness ofthe importance of biosecurity in a tangible way that most people understand. Soiled boots must becleaned thoroughly by scrubbing, perhaps using adilute detergent solution and all gross faecal mattershould be removed before immersing them in the dis-infectant. Combined boot brushes/washers are useful,but can become heavily contaminated and requireregular cleaning. Disinfectant mats are somewhat cosmetic unless the solution is regularly replenishedand any build up of faecal contamination is removed.However, they also increase awareness and are worthconsidering outside relatively clean areas such as theentrance to off-site farm offices or changing rooms.

Combined boot brushes and footbaths can become heavilycontaminated

numerous factors such as the type of pathogen, numberand density of animals excreting and susceptible toinfection, housing, droplet size, humidity, ambient tem-perature, ventilation fans, wind strength and direction,sunlight and topography. In France, the danger ofaerosol spread when spraying slurry onto agriculturalland is well recognised and, hence, slurry injection isrecommended instead of surface spreading.

HERD LOCATION

Geographical location, particularly proximity to otherlive pigs, is probably the overriding factor which dictatesthe risk of a herd acquiring new disease. The type, num-ber and density of pig units in a 2 km radius are crucial.The position of major roads, prevailing wind direction,drainage, vegetation and biosecurity measures adoptedon nearby premises are all significant. Ideally, new pig

units should be sited in areas of low pig density awayfrom obvious risk factors such as other pig herds,slaughterhouses, slurry lagoons, refuse tips and roadsused by pig transporters. However, for commercial reasons, pig production in Britain and elsewhere is concentrated in a few regions where endemic diseasesare inevitably prevalent.

A minimum distance of at least 500 m between pigfarms may reduce the risk of acquiring common infec-tions but, in many commercial herds in high pig densityareas, it is very difficult or impractical to maintain disease freedom from common endemic diseases such as PRRS, EP, SI and, particularly, PMWS. This is noexcuse for poor biosecurity, but an appreciation of whatis realistically achievable is essential. For some diseases,the use of vaccination (if available) may be more appro-priate and cost effective than relying solely on otherbiosecurity measures which are impractical due to fac-tors beyond the owner’s control.



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VEHICLES, EQUIPMENT ANDCONSUMABLES

Contaminated vehicles (particularly those used to trans-port livestock) and their drivers represent an importantmeans of disease transmission, as was evident during therecent outbreaks of FMD in Britain and CSF in Holland.

Vehicles, trailers and other equipment should befarm-dedicated, if possible. The degree of risk dependson how recently the vehicle has been used on other pigor livestock farms or for conveying pigs from market to the slaughterhouse. The increasing trend towards two-and three-site production systems has led to more trans-portation of live pigs. Transporting finishers to slaughterin the morning and weaners in the afternoon leavesinsufficient time between journeys for satisfactory clean-ing and disinfection. Adopting a three-week batch wean-ing system reduces the need to move pigs as frequentlyand facilitates the all-in, all-out approach, which pro-motes good hygienic practice.

External vehicles should not be permitted onto a farmunless essential (eg, for urgent repairs). These vehiclesmust be visibly clean, washed and disinfected undersupervision on hard standing areas off-site. The effec-tiveness of this approach was demonstrated during therecent FMD epidemic in Britain. Particular attentionshould be paid to wheel arches and the underside of thevehicle. It is also important to ensure that personnel donot become contaminated during washing – disposableplastic boots should be worn, if practicable. Vehiclefootwells or floors inside the lorry cab are difficult toclean and disinfect adequately, although the provision ofrubber mats and disinfectant sprays may help. Fixedwheel washes are helpful if they are of good design, but

disinfectant mats for vehicles are of limited value andsoon become heavily contaminated.

Feed lorries must be visibly clean and make deliver-ies from outside the perimeter fence or at the peripheryof the farm using farm-dedicated blower pipes. High-health status and nucleus units should try to arrange feeddeliveries for the first drop of the day at the beginning ofthe week. Contractors’ boxes and equipment that mighthave been used on other livestock premises should bedisinfected.

The anteroom or office delivery point area close tothe main entrance to a farm is a potential focus for conta-mination by pathogens on cardboard containers used foritems such as pharmaceutical products or semen coolers.Surface disinfection and hygienic disposal of packagingshould therefore be instituted, as appropriate.

Livestock loading and unloadingLoading and unloading of live pigs are procedures whichoffer opportunities for new infections to be introduced

Thorough cleaning ofvehicles, particularly wheelarches, played a crucialrole in limiting the spreadof infection during the2001 FMD epidemic inBritain

Vehicles presenting a biosecurityrisk

■ Vehicles delivering and collecting live pigs■ Vehicles delivering feed ■ Employee vehicles■ Engineers’ and maintenance services’ vehicles■ Vehicles delivering bedding ■ Waste removal vehicles■ Vehicles collecting dead pigs■ Vehicles delivering equipment, pharmaceuticalproducts and semen

In Britain, the Pigs (Records, Identification and Move-ment) Order 2003 (PRIMO) and The Disease ControlOrder 2003 require a 20-day standstill period whenpigs move to another herd. However, nucleus, multi-plier, grow-out and weaner-breeder herds can applyfor exemption from the 20-day rule if they restricttheir sources of breeding replacements to approvedherds higher up the pyramid. They must also demon-strate high standards of biosecurity.

A well designed and easily cleaned loading bay with gooddrainage facilities

A farm-dedicated pig transporter is ideal, but it should becleaned and disinfected if it is used off the farm or betweenunits



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by infected stock or fomites (contaminated vehicle,equipment or clothing). Vehicles delivering pigs shouldbe thoroughly cleaned and dried before transporting pigsonto a unit. Pig transporters should not be allowed ontothe main farm premises, if possible – a purpose-builtloading bay with good washing, disinfecting anddrainage facilities, located as far away as practicablefrom pig accommodation, is ideal. Outgoing pigs shouldbe moved into the loading bay, with farm staff observingstrict clean and dirty area protocols to avoid contact withthe collection vehicle. The loading bay and surroundingarea should be kept clean and disinfected.

HUMANS

The potential for the transmission of infectious aerosolsby humans appears to have been greatly exaggerated. Apolicy of two or three pig-free days or ‘downtime’ forvisitors and veterinary surgeons is widely imposed, particularly on high-health status and nucleus breedingunits. This concept has its origins in work undertaken inthe 1970s on the persistence and transfer of FMD virusfrom the mouth and nose of humans 28 hours (but not 48 hours) after exposure. However, contrary to commonperceptions, recent scientific evidence – particularlyfrom the USA – and field observations from experiencedresearch workers suggest that the likelihood of peopleactually transmitting pathogens from their nose, mouthor pharynx is minimal. Imposing a blanket downtimerequirement causes great inconvenience and is expensiveto maintain.

Nucleus herds and others of high-health status willunderstandably wish to maintain 48 to 72 hours down-time as an insurance policy and a deterrent for unwantedvisitors. Where possible, it is prudent for veterinary sur-geons and other essential farm visitors to attend herdshigher up a breeding pyramid at the beginning of theweek. However, it is important that such measures arekept in perspective and do not assume more importancethan they merit. Provided a visit to a pig herd is followedby a complete change of clothing, showering, hand (par-ticularly fingernails) and hair washing, and nose blowing,a single overnight pig-free period of at least 12 hours, as now suggested by several authorities, should be morethan adequate for most situations assuming other precau-tions are adopted. Notifiable disease outbreaks are anexception and are covered by national rules. Additionalshowering-in on arrival may be unnecessary, but itincreases awareness and presents a useful physical barrierin that street clothes are replaced by dedicated clothing.

In selected circumstances, if there are major concerns, theadditional use of a disposable paper dusk mask thatadheres to British standard EN149 with the highest (P3)dust protection factor may be worth considering.

Formulating basic biosecurity rules for visitors(including vehicle drivers) and farm employees costs little and can greatly reduce the risks of introducinginfection by fomites, including dirty boots, contaminatedclothing or personal equipment. Protocols will inevitablyvary with the type of unit and circumstances, being high-er and more onerous on high-health status nucleus herdsat the top of the breeding pyramid and during notifiabledisease outbreaks.

FEED, WATER AND BEDDING

Salmonella species may potentially be introduced by contaminated feed (in addition to the risk of feed deliv-ery vehicles acting as fomites). Feed should be obtainedfrom mills operating in accordance with relevantDEFRA and Agricultural Industries Confederation codesof practice and using ingredients obtained from sourceswith a consistently satisfactory bacteriological record.There is a small risk of acquiring infection (mainlySalmonella species) from contaminated water. Ideally,

Biosecurity precautions for farm workers and visitors

■ Provide staff training programmes on biosecurity and hygiene■ Institute standard operating procedures and check compliance regularly(using HACCPs)■ Apply reasonable, but strict, protocols after contact with other pigs ■ Ensure good personal cleanliness (hands, fingernails, hair) ■ Provide farm-dedicated protective clothing and boots or insist on spotless and disinfected boots/clean washable protective clothing■ Consider using hats and disposable plastic gloves■ Do not allow visitors (excluding veterinary surgeons and similar) to approachor handle stock ■ Use farm-dedicated equipment, notebooks (washable), mobile phones, and so on, or adopt a disinfection protocol (laptops, etc) between visits■ Keep office and staff accommodation clean and uncluttered■ Be aware of potential disease risks linked to international travel■ Do not allow any pig products or other unauthorised material onto the farmor into the canteen■ Ensure that human food is eaten only in the staff canteen or dedicated area(also see above)■ Make sure visitors/employees sign a book (see below) to confirm that precau-tions have been undertaken■ Adopt strict protocols for loading/unloading pigs, carcase disposal, and so on

Information to be recorded in avisitors’ book

■ Date■ Name of visitor■ Company name/address■ Purpose of visit■ Date of last contact with pigs■ Time of arrival■ Time of departure■ Signature to confirm that biosecurity precautionshave been observed

An appropriate and effective loading bay on an outdoor unit



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diseases including TGE, Streptococcus suis infection andPRRS, but control can be problematic.

The increasing number of feral wild boar in someparts of Britain, and the potential for their expansion intonew areas, pose very specific disease threats to outdoorherds – as recently illustrated by the CSF outbreaks inseveral European countries, such as Luxembourg. Com-mercial wild boar production units must be licensedunder the Dangerous Wild Animals Act 1976 and secureescape-proof perimeter fencing is essential. Conven-tional pig units in the vicinity need to adopt heightenedprecautions.

Carcase disposal

Disposal of carcases has always been a potentialproblem, particularly on units experiencing high mor-tality during severe outbreaks of disease such as TGEor PMWS. Difficulties have increased following theimposition of The Animal By-Products Regulations2003, which prohibit on-farm burial and pig disposalpits. A new National Fallen Stock Scheme with achargeable farm collection service started operatingat the end of 2004. This has major biosecurity implica-tions and, ideally, requires a separate isolated pre-collection carcase storage facility on a concreted area,which can be easily disinfected, located at the periph-ery of the farm. Instead, many farmers may preferon-farm incineration. Low capacity incineration units(for burning less than 50 kg of animal by-products an hour), inspected and approved by the StateVeterinary Service, may be suitable. For further infor-mation on carcase disposal, see the DEFRA website.

Slurry disposal and waste management

If a slurry pit is to be used, it should be largeenough to hold four to six months’ of waste toreduce the need for frequent emptying. Ideally, thepit should be positioned outside the unit with chan-nels running from different buildings. Storing slurryfor as long as possible (at least four weeks, prefer-ably several months) will kill most Salmonellaspecies and other organisms. Farm-dedicated vehi-cles should be used for slurry removal. Solid manureshould be stacked and composted in fenced padsbefore spreading it onto arable land. If slurry is tobe spread onto pasture, pigs should be kept off theland for at least three weeks.

Essentials of vermin control

■ Adopt a regular, effective pest control programme (using a contractor or in-house)■ Ensure frequent and correct baiting and inspection■ Adopt intensive baiting when pens are empty■ Review house design, farm layout and generalhygiene procedures■ Reduce favourable habitats for wildlife (weedovergrowth, rubbish and debris)■ Avoid feed spillage – if spillages do occur, ensure that they are cleared up promptly; cover feed barrows ■ Repair buildings to prevent access and nesting,and remove refuge sites

Wild boar farms require very secure perimeter fencing

Disposal of dead pigs is an important issue withsignificant biosecurity implications

mains water should be used; water from boreholes and wells should be tested regularly for bacteriologicalquality.

The risks of straw, shavings and other bedding sub-strates acting as fomites should be reviewed. Thesematerials should not come from sources which mighthave been exposed to livestock or excrement, and shouldbe stored under cover and protected from contaminationby birds or vermin.

WILDLIFE AND VERMIN

The risk of rodents, feral cats, birds, insects and otheranimals acting as vectors of disease is much more diffi-cult to control than disease spread by humans, equipmentand vehicles. TGE virus was notorious in Britain for itstransmission by starlings and gulls, especially on out-door units and in uncovered feeding areas. Completebird proofing was attempted with partial success onsome pig farms during the TGE epidemic of 1980 to1983 in Britain. Other infections spread by birds includesalmonellosis and avian tuberculosis (via infected peatused as bedding). Even on outdoor units, practical mea-sures such as installing rubber flaps on feeders reducedisease risks and also allow considerable savings in feedcosts. Mechanical transmission by insects, particularlyflies, has been implicated in the spread of several



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Outdoor pigs are inevitably exposed to Leptospiraserovars, particularly Leptospira bratislava, from vari-ous wildlife species including hedgehogs, foxes and rats.Rodents can introduce disease such as Salmonella infec-tion (which is also spread by feral cats), swine dysenteryand Lawsonia intracellularis infection. As with birds, alarge rodent population represents a significant amountof food wastage, which is an added incentive for control,even on outdoor units. Independent consultancy adviceon pest control is available from organisations such asADAS. It is advisable not to allow domesticated petsonto the farm premises, but if guard dogs are used theyshould not be fed marrow bones. The veterinary surgeonshould also remain alert to potential disease transmissionrisks from domestic cats.

VALUABLE INITIATIVES

The pig industry has been very proactive in promoting thebenefits of biosecurity and implementation of its Strategyfor British Pig Health and Welfare, launched in December2003. As part of this initiative, the National Pig Associ-ation (NPA) and BPEX have developed (funded byDEFRA) a personalised self-assessment audit to help producers improve biosecurity on their own farms. Thisshould become available on the NPA website during 2005.Such an approach offers an ideal starting point for veteri-nary surgeons and producers seeking to identify cost-effec-tive measures appropriate to particular farm circumstances.

AcknowledgementsThe authors would like to thank veterinary and DEFRA colleagues,and members of the pig industry for their valuable comments andfor the use of the illustrations appearing in this article.

Close contact between pigs and birds on outdoor unitsinevitably presents increased disease risks

Rubber flaps on outdoor feeders help to discourage wildbirds

Feral wild boar pose a significant risk to outdoor pig units Perimeter fencing should be secure to prevent the escapeand entry of feral wild boar or other pigs

Further readingAMASS, S. F. (2002) Biosecurity: what does it all mean? Proceedingsof the 33rd annual meeting of the American Association of SwineVeterinarians. Kansas City, March 2 to 5. pp 279-281DEE, S. A. (2003) Biosecurity: a critical review of today’s practices.Proceedings of the 34th annual meeting of the AmericanAssociation of Swine Veterinarians. Orlando, Florida, March 8 to 11. pp 451-454WRATHALL, A. E., SIMMONS, H. A., BOWLES, D. J. & JONES, S. (2004)Biosecurity strategies for conserving valuable livestock geneticresources. Reproduction, Fertility and Development 16, 103-112

Further informationPIG WORKING GROUP OF THE RUMA ALLIANCE (1999) Responsibleuse of antimicrobials in pig production. (Revised 2004)BRITISH PIG EXECUTIVE (2004) ZAP Salmonella Programme:Salmonella Control UpdateDEFRA (2000) Code of Practice for the Prevention and Control ofSalmonella on Pig Farms

Websites■ DEFRA: www.defra.gov.uk■ British Pig Association: www.britishpigs.org.uk■ National Pig Association: www.npa-uk.net■ British Pig Executive: www.bpex.org■ ADAS: www.adas.co.uk

CORRECTION

Heartworm and lungworm in dogs and cats in the UK (In Practice, March 2005, pp 147-153)On page 147, under the section on Angiostrongylus vasorum, the first sentence should have read ‘Angio-strongylus vasorum is a metastrongyloid nematodewhich inhabits the right ventricle and pulmonary arter-ies of its definitive host, the dog and related Canidae.’,and not as stated. The author regrets the error.



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biosecurity: reducing disease risks to pig breeding herds · pig producers have probably suffered...

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