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On Farm Biosecurity |
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José Barceló, Enric Marco, B&M, C.V.P., Valldoreix, Barcelona, Spain IntroductionGenerically speaking biosegurity means "life security". By on farm biosecurity we refer to the application of health controls and measures to prevent the introduction of new infectious diseases into herds and to avoid their spreading. All too often we undervalue the importance of biosecurity. The ignorance of many diseases and the existence of many others with different individual epidemiologies could be the cause of certain incredibility that often has serious consequences. However, this possible ignorance quite often turns into fear leading to the adoption of exaggerated biosecurity measures that finally are not applied. The health status of a herd should not condition the introduction and application out of biosecurity measures. A low health status does not justify the lack of such measures as the possibility of new diseases always exists. Although there are many references that demonstrate contamination of new diseases due to the of lack of biosecurity measures, it is possibly situations such as the recent outbreaks of Classical Swine Fever (CSF) in Holland, Spain and Germany that confirm that biosecurity standards should always be maintained as we never know what may happen in the future. In high-density areas, only by assuming collective responsibilities may we achieve acceptable levels of health security. The most important factors to bear in mind in the prevention of possible new diseases are, in this order: location, isolation of replacement stock and the conditions of the farm itself. 1. LocationThis should be considered to be the most important factor within biosecurity. Only an isolated location will prevent the introduction of airborne diseases. In optimal climatic conditions (winter, high humidity level, constant moderate winds, flat land) windborne dust or aerosol droplets present in the air can infect the animals. Nowadays there is evidence that Foot-and-mouth disease (FMD) (1,2,3) and Aujeszky’s disease (AD) (4,5,6,7) can travel long distances and that Enzootic pneumonia (EP) (8) and PRRS (9) can be airborne within a 4 Km.radius. In view of these circumstances, herds situated in high-density areas should accept their condition of carriers of these diseases should they be present in the area. The fact that there is no clear evidence regarding other diseases such as CSF, African Swine Fever (ASF), Transmissible gastro-enteritis (TGE), or infectious bacterial diseases such as Atrophic rhinitis (AR),•Swine dysentery (SD), PED, Pleuropneumonia, Leptospirosis and others, does not mean that airborne transmission over short distances is not possible (<100 m.) (10). The application of strict biosecurity measures in herds situated in high-density areas is possibly the only available alternative for the prevention of some of these diseases. A well isolated herd has greater possibilities of maintaining its health status and may enlarge its population without increasing the risk of new diseases provided that biosecurity rules are followed. Due to their importance in the production chain, herds belonging to breeding companies should pay special attention to location. A bad location could be responsible for infections such as EP, PRRS, AD, etc. and so increase the possibility of selling animals with undesirable diseases. It is essential to carry out a detailed study of the possible location before starting up a new unit. The following parameters should be taken into account, in this order, when assessing possible locations: • Pig farms nearby: A farm with 500 animals (sows, piglets and fatteners) at a distance of 1 km. represents less risk than a herd of 5,000 at 2 km.
The ideal location would be: "A herd situated in low pig density locality and region, in a hilly area or close to the sea, on a hill if the climate is warm and protected from winds in cold humid climates, situated at least 3 km. from other swine herds and other risk factors, other pig farms should not be visible." 2. Isolation for replacement stock The control of the introduction of replacement stock (gilts and boars) at 100 Kg. 2. Isolation for replacement stockThe control of the introduction of replacement stock (gilts and boars) at 100 Kg. or less is basic in order to maintain a stable health status. The purchase of animals should not be responsible for contamination by new infectious diseases. The health status of the source farm should always be superior or equal to that of the receiving herd. In general terms we could say that the larger and "healthier" a farm, the greater the risk of introducing new diseases. Large herds have a greater need for replacing stock and several diseases may contaminate healthy farms. In both cases, strict biosecurity measures should be applied. The isolation of replacement stock allows us to detect diseases in the incubation phase in the source farm, check for the presence of chronic diseases and even eliminate infectious agents through medication before the animals are introduced into the herd. Three very important factors should be taken into account when introducing new stock: the health status of both the source farm and the receiving farm (fig.1) and conditions in the isolation building. A professional and trusting relationship between the veterinarians responsible for the two farms is always desirable. The following points should be considered when setting up an isolation unit:
Herds in countries or areas in which CSF, ASF or FMD are present should consider the use of two isolation units: a quarantine building outside the farm perimeter fence and an acclimatisation building inside. Reducing the frequency with which new animals are introduced by entering pigs with different weights should also be considered. 3. The farmThe health status of a farm conditions to a great extent the introduction and application of biosecurity measures. Herds situated in high-density areas are submitted to a greater risk of new diseases and consequently should adopt biosecurity measures in order to protect their animals. As for breeding companies, these measures should be stricter and more intense at the top of the genetic pyramid. Over the years it has been proved that the correct application of suitable biosecurity measures is an efficient way of preventing new diseases. However, outbreaks of new diseases in farms with exceptional biosecurity measures and which are difficult to explain, emphasise the fact that gaps still exist in this area. The acceptation and correct following of biosecurity measures by everyone implicated on the farm is a crucial factor. Human failure is in many cases responsible for new infections. Although it may appear to be a contradiction, quite often farm owners and veterinarians are the first to relax when applying biosecurity measures. Many are the factors involved in the biosecurity of a swine herd. When starting up a new farm, the distribution of the buildings should be planned to determine initial health protection and optimise the movement and welfare of the animals. When planning a large herd (more than 700--1,000 sows) the possibility of carrying out the weaning and fattening phases on separate sites should be considered. Risks to be considered in the biosecurity of the farm are:
Non-moveable risks. These include loading bay, fencing, main entrance, changing facilities and office. Loading bay: This represents the greatest risk. The fact that on many occasions it is impossible to control the correct washing and disinfecting of the lorries means that the loading bay acquires an enormous importance. Pig transport vehicles and drivers should be regarded as a major risk as they are in constant contact with other farms and slaughterhouses. The loading bay should clearly define a clean zone and a dirty zone. Under no circumstances should drivers have access to the clean area. The same criterion should be applied to those animals that have been in contact with the dirty zone or have been loaded onto the lorry. When in doubt as to the security of washing or disinfecting of vehicles, farm owners should insist on a down time period, this being an obligatory measure in the case of breeding units. An adequate loading bay should be situated more than 20 m. from the building housing the animals and there should be one-way gates and ramps to prevent the re-entry of animals and liquids. It should be possible to clean and disinfect the bay in such a way that liquid and solid remains drain away outside the perimeter fence. Separate bays for loading animals entering and leaving the farm are always best. Finally the bay should be covered as this facilitates the correct handling of the animals particularly in the case of rain, snow or excessive sunlight. Fencing: This should be complete and clearly differentiate the internal area (clean) and the external area (dirty). The fencing may include natural barriers, for example cliffs or rivers, and man-made barriers such as the wall of a closed building. In general the fencing should prevent the entry of animals or people. In certain circumstances it may be necessary to build a solid, high fence to prevent the entry of wild animals such as wild boars or a high double fence to keep out determined intruders. Main entrance: The main and other entrances must remain closed. A sign reading "No entry for health reasons" should be erected. Other measures included in this section are: presence of call-bell, car park and written instructions for visitors. Registers should be used to control visitors and the movement of vehicles transporting feed, animals, slurry or solid excrements and other materials such as straw, sawdust or construction material. Not only are these registers useful in preventing disease but can also be used for epidemiological studies in cases such as CSF and ASF.•Changing facilities and office: The changing facilities and office should be situated within the main perimeter fence. Showers or an intermediate area (e.g. Danish SPF herds) should mark the clean area of the changing facilities. The changing facilities should be kept clean and boots, overalls and hats should be provided. The office should be situated in the clean area in which case a communication hatch with the exterior will be necessary for exchanging documents etc. Should workers eat on the farm, a canteen next to the office in the clean area will be needed. Under no circumstances should personnel and staff be allowed to eat outside the canteen and the consumption of pork or its by-products should be prohibited as these can transmit viruses such as CSF, ASF, and FMD. Moveable risks Feed, waste management, other materials, water, and people. Feed: This should be loaded from outside the fencing. Its components should be from safe, known sources. Different vehicles should be used for the transport of cereals and animals. In breeding units unloading first thing Monday morning assures greater biosecurity provided that the vehicles have undergone a down time period over the weekend. When unloading is by suction, the tube should belong to the farm to avoid contact with other farms. Waste management: Slurry disposal normally causes biosecurity problems. When working with liquid slurry, channels running from the different farm buildings into a pit outside the compound fence are recommended. The level of slurry in the pit should always be inferior to that of the different channels to avoid a flow back of slurry when removed with suction pumps. The pit should be able to hold 4--6 months slurry production in order to optimise the use of the product in agriculture and to reduce the need for frequent disposal when working with large capacity lorries. In the case of solid manure, disposal is more problematic and various fenced pads against the compound fence are needed with the central pad acting as a health alternative. In both cases, the possibility of removing slurry with farm owned vehicles reduces the risk of contamination. Other materials: The unloading of straw, sawdust, shavings, paper or a mixture of these along with other bedding materials must be carried out through the fence. They should then be correctly stored to prevent birds defecating on them as starling faeces, for example, can spread the TGE virus. Water: The water supply should be sufficient to avoid the need to use other sources that cannot be controlled. The quality of the water should be acceptable and disinfection systems must be used should it not meet minimum bacteriological requirements. People: The part played by people in the transmission of disease and ways of reducing risks have been the subject of numerous discussions, for example the convenience or not of the obligatory use of showers. It is curious to observe that in emergency situations, for example the outbreak of a notifiable disease, this discussion disappears. In Spain the transmission of CSF by people during the•recent outbreaks has been confirmed. People visiting several farms a day have proved to be an important source of contamination. The diseases present in an area or region and the number of visits carried out are two important factors that determine the risk of disease transmission by people. As for farm workers and staff, the possible contact outside the herd (own pigs, markets, fairs, and slaughterhouses) and their cohabiting with people working on other farms represent a risk. It is a known fact that people can transmit Gastro-enteritis and FMD (12). It is very possible that the use of footwear and clothing exclusive to the farm may be sufficient to avoid infection. However, due to the reasonable risk of infectious disease transmission and the high investment made in the farm, showering and a change of clothes before entering is always recommended. In the case of breeding companies, visitors should be kept to a minimum and they should be obliged to shower and to respect the established down time period before entering the farm. Internal risks Pest control, domestic animals, pig disposal and sick animals. Pest control: Rats, mice, birds and flies. The control of rats and mice is a difficult task. An adequate construction and maintenance of the farm facilities and a "clean" external aspect, the prevention of access to feed and water, and the use of traps and rodenticides are some alternatives. Bird proofing nets in windows and other openings limit the entry of birds although their control in open-sided buildings or outdoor pens is very difficult. The cleaning of pits, the use of insecticides and correct ventilation are some systems for the control of flies. Pig disposal: The pit for dead animals, incinerator or collecting point must be situated outside the main compound fence. The pit should be deep and not allow the access of animals (dogs and cats) or birds. The collection of dead animals should be suspended if notifiable diseases are present in the area. Sick animals: All farms should have a small, isolated and comfortable building for sick animals. Humane methods must be used for the sacrifice of sick pigs. The area reserved for post-mortems should be situated outside the fence and should be easy to clean. Health management procedures Routine, an excessive workload, low production figures and a lack of mentality are some of the factors that may lead to relaxation in health rules. The completion of health questionnaires three or four times yearly is a great help in keeping workers on their toes. Regular, programmed visits by a veterinarian swine specialist to revise, control and advise on vaccination programmes, medication, management systems for disease control, post-mortem registers, cleaning and disinfection programmes, blood sampling, etc, along with regular slaughterhouse checks are important in maintaining biosecurity measures and health control.•Animal welfare Adequate nutrition, housing and management procedures are vital in order to maintain animal resistance to infections. The control of existing diseases depends on the maintenance of good body condition, the general cleaning of buildings, the strict following of management routines, the correct handling and optimal stocking densities. Otherwise disease could become uncontrollable. Fig. 1. Some of the methods and systems available for checking the health status of source and receiver farms.
1)Sellers, R.F and Gloster, J. (1966) The Northumberland Epidemic of foot-and-mouth disease, 1966, J. Hyg, Camb. 85: 129-140 2) Gloster, J., Blackall, R.M., Sellers, R.F. and Donaldson, A.I. (1981) Forecasting the airborne spread of foot-and-mouth disease. Vet. Rec., 108, 370. 3) Gloster, J., Sellers, R.F., and Donaldson, A.I. (1982) Long distance transport of foot-and-mouth disease virus over the sea. Vet. Rec., 110, 47-52. 4) Gloster, J., Donaldson, A.I. and Hough, M.N. (1984) Analysis of a series of outbreaks of Aujeszky’s disease in Yorkshire in 1981-82: The possibility of airborne disease spread. Vet. Rec., 114, 47-52. 5) Christensen, L.S., Mousing, J., Mortensen, S., Sørensen, K.J., Strandbygaard, S.B., Henriksen, C.A. and Andersen, J.B. (1990a) Evidence of long distance airborne transmission of Aujeszky’s disease (pseudorabies) virus. Vet. Rec., 127, 471-474. 6) Christensen, L.S., Sørensen, K.J., Stranbygaard, B.S., Henriksen, C.A. and Andersen, J.B. (1990b) Evidence of long distance airborne transmission of Aujeszky’s disease virus. I: Identification of emerging strains. In Proc. IPVS Lausanne, Switzerland, 206. 7) Christensen, L.S., Standbygaard, S.B., Henriksen, C.A., Andersen, A.B. and Andersen, J.B. (1989) Aujeszky’s disease in Denmark: The epizootiological situation in winter 1987-88 studied by restriction fragment pattern analysis. Saertryk af Dansk Veterinaertidss Krift, 72, 322-325. 8) Goodwin, R.F.W. (1985) Apparent reinfection of Enzootic pneumonia free pig herds: Search for possible causes. Vet. Rec., 116, 690-694.•9) Robertson, I.B. (1992) New pig disease up date: epidemiology of PRRS. Pig Veterinary Journal, 29, 186-187. 10) Alexander, T.J.L. (1991) Transmission y control de enfermedades en cerdos. Simposio internacional de porcino-cultura, Murcia, 120-129. Edited by the Consejería de Agricultura, Ganadería y Pesca de la región de Murcia (Spain). 11) Vraa-Andersen, L. (1994). A case control study of risk factors for infection with Actinobacillus pleuropneumoniae serotype 2 in Danish SPF swine herds. In Respiratory diseseases in Danish slaughterswine, application of epidemiological methods. Ph. D. Thesis, Denmark, 1994 12) Alexander, T.J.L. and Harris, D.L. (1992) Methods of disease control. In Disease of swine 1992 7 th edition. 808-836. Edited by A.D. Leman and others. Iowa State University press, Ames, Iowa, U.S.A. 13) Muirhead, M.R., Alexander, T.J.L. (1997). Understanding disease. In Managing pig health and the treatment of disease 1997 1 st Edition 21-52. Edited by T.J.L. Alexander, 5.M. Enterprises Ltd., Sheffield, U.K. ACKNOWLEDGEMENTS Our thanks to Bridget Lester, our secretary, for translating this paper into English.
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