77 Biosecurity
The term ‘biosecurity’ includes a wide range of measures aimed at preventing or limiting exposure of domesticated animals to microbial pathogens from outside sources or to infectious agents shed by infected animals within the herd. These measures are important for the prevention and control of infectious diseases (Box 77.1). Effective management practices which prevent the spread of pathogens from infected animals to susceptible animals and that prevent the introduction of infected animals or microbial pathogens into a herd or region of a country where a disease does not occur, minimize the risk of such diseases occurring in susceptible livestock. Benefits of an effective biosecurity programme include a high standard of animal health and welfare, freedom from specific pathogens, improved animal production and reduced production costs. An effective biosecurity programme has many components, all aimed at ensuring that the risks of healthy animals acquiring infection are minimized. These include the design, location and environment of farm buildings, policies relating to the purchase of replacement animals, feed supplies, regulation of employees, transport vehicles, service personnel and people visiting the farm with or without prior appointments (Table 77.1). The larger the operation, the greater the need for effective biosecurity measures.
Table 77.1 Biosecurity for farm animals.
| Component | Considerations | Comments |
| Animals | Replacement animals should be purchased from reputable sources | Newly purchased animals should be isolated and closely monitored for at least 2 weeks |
| Feed | Close attention should be given to source and quality of feed | Feed can become contaminated by wild birds and rodents during storage |
| Water supply | Source and quality of water should be evaluated | Drinkers within buildings and water troughs for grazing animals can become contaminated with faeces or urine |
| Vehicular and pedestrian traffic | Delivery vehicles should conform to farm's standard of hygiene; staff, service personnel and visitors should wear protective clothing and waterproof footwear and use footbaths provided | Particular care is required with vehicles used for transportation of animals, slurry tankers and vehicles used for disposal of bedding material |
| Farm equipment | Sharing of farm equipment and vehicles for transportation of animals should be avoided | Equipment used for cleaning farm buildings or spreading animal waste should not be borrowed or loaned |
| Animal waste | Liquid animal waste should be stored in slurry tanks; solid animal waste should be composted on the farm and spread on arable land | An interval of 2 months should elapse between the application of slurry to pasture and commencement of grazing |
| Wildlife, including rodents and wild birds | When wildlife and grazing domestic animals live in close association, wildlife can transmit microbial pathogens to domestic animals; rodents can act as reservoirs of microbial pathogens and wild birds can transmit viral and bacterial pathogens to commercial poultry flocks | Wild birds should not have access to poultry houses or feed mills and buildings should be designed to exclude rodents |
| Cleaning and disinfection | Thorough cleaning followed by disinfection is essential for the elimination of microbial pathogens from farm buildings, transport vehicles and equipment | Although effective cleaning can reduce the number of microbial pathogens in a building, chemical disinfection is required to inactivate residual microbial pathogens |
Ensuring that the domestic animal population within a country remains free of major infectious diseases is a constant challenge for national and local veterinary personnel and staff in diagnostic laboratories. Exclusion of suspect animals from a country, quarantine at point of entry, isolation of infected and in-contact animals on the farm, followed by diagnostic testing and, if necessary, slaughter are widely applied measures for the control of exotic infectious diseases in animal populations. Free movement of animals between countries or within a country also invariably leads to free movement of microbial pathogens. Because movement of vehicles and animals is an unavoidable feature of stud farms, it is important to ascertain the health status of mares and stallions used for breeding purposes. There are inherent risks associated with the movement of breeding mares onto a farm. Such animals should have their vaccination status confirmed in advance of acceptance by the stud farm and be certified free of Taylorella equigenitalis. Streptococcus equi is a constant source of concern when horses are brought together for breeding purposes, for competitive events or for sales. A thorough clinical examination together with a detailed clinical history of each animal may aid in the detection and exclusion of suspect animals at the point of arrival.
Replacement animals should be purchased from reputable sources where the history of the herd or flock from which they derived is known. Imported animals should be quarantined at point of arrival in a country and subjected to thorough clinical examination combined with appropriate laboratory test procedures. A limitation of both quarantine and isolation of animals after purchase relates to diseases with long incubation periods such as paratuberculosis in cattle, scrapie in sheep and rabies in dogs and cats. Because latent viral infections and latent bacterial infections may not be detectable by clinical examination of animals, serological tests and collection of specimens for culture or virus isolation may be required to detect a carrier state in apparently healthy animals.
The harmonious relationship between animals and their environment can be reinforced by good management systems, optimal nutrition, adequate floor space and effective disease control programmes. Factors that can adversely affect animals' wellbeing include overcrowding, uncontrolled environmental temperature, nutritional imbalances and absence of a well designed and implemented disease control programme. Buildings, farmyards, paddocks and other grazing areas can be planned so as to promote animal health. Conversely, improper building design, inadequate ventilation and insufficient floor space for the animal population can predispose to stressful environmental conditions for intensively-reared animals. Careful temperature control is a requirement for neonatal pigs and newly hatched chicks. Building design should incorporate features which facilitate cleaning and disinfection at the end of a production cycle or following an outbreak of infectious disease. Floors and walls with a moderately smooth finish facilitate cleaning and minimize trauma to animals without predisposing to slipping. On large farms, consideration should be given to the inclusion of facilities for washing and disinfecting vehicles for transportation of animals. Dusty paddocks and heavily grazed pasture can lead to a build-up of Rhodococcus equi which can result in suppurative bronchopneumonia in foals up to four months of age. Rough pastures provide cover for many tick species such as Ixodes ricinus. The acquisition of tick-borne diseases such as louping ill and tick-borne fever is usually associated with animals grazing rough pasture.
The source and quality of feed for farm animals requires careful consideration to ensure freedom from microbial pathogens or toxic factors. Feed such as grain can become contaminated during storage with viral or bacterial pathogens before it reaches feed mills. Wild birds and rodents have been implicated in feed contamination and cats shedding oocysts of Toxoplasma gondii in their faeces can contaminate grain in feed mills or on farms. Animal-derived protein should be excluded from the diets of ruminants due to the association of BSE in cattle with the feeding of meat-and-bone meal. Crops grown by the owner on the farm are sometimes the source of infectious agents or biological toxins. Listeria monocytogenes can replicate in the surface layers of poor-quality silage and produce listeriosis in ruminants. Botulism in farm animals has been associated with feeding baled silage and with the landspreading of poultry litter.
The source and quality of water for farm animals may be influenced by farm location, climatic factors and other environmental influences. Contamination of a clean water supply on a farm can occur due to faecal or urinary shedding of pathogens into drinkers in buildings. For grazing animals, ponds or larger bodies of water may become contaminated by run-off from slurry spreading or overflowing slurry tanks. Wildlife, either resident or migratory, can contaminate ponds with enteric pathogens or leptospires. If poultry houses are located close to lakes or large ponds, migrating waterfowl or seabirds can transmit avian influenza or Newcastle disease to domestic poultry.
Control of vehicles calling at farms requires close surveillance. Particular attention should be paid to vehicles used for collection of animals, slurry tankers and other vehicles used for disposal of animal waste. Staff working on farms, service personnel, veterinarians and others on official business should adhere strictly to wearing protective clothing and footwear at all times. Footbaths, strategically positioned for pedestrians, should be used by all persons entering the farm. To ensure compliance with footbath use, all pedestrians entering the premises should wear clean, waterproof footwear. A secure perimeter fence is an essential component of any biosecurity system. Footbaths should be large enough to accommodate the largest size of footwear worn by workers or visitors. Disinfectants suitable for footbath use include iodophors, phenolic compounds and formalin. If a specific infectious agent is identified as the cause of a disease outbreak, a disinfectant known to be effective against that agent should be used in all footbaths on the premises.
Wheel baths are sometimes positioned at farm entrances as part of a disease control programme. The design of wheel baths should be such that there is adequate contact with the disinfectant for a sufficient time to ensure the inactivation of infectious agents on wheel surfaces. The tyre of the largest vehicle wheel entering the bath should be completely immersed in one revolution. Installation of a properly designed wheel bath is expensive and may impart an unrealistic impression of biosecurity. In many instances, the contents of vehicles including animals, their excretions and secretions, animal feed and bedding pose a greater threat of transferring infectious agents than vehicle wheels.
In buildings with slatted floors, animal waste is stored in slurry tanks. Such tanks should be constructed to high specifications and have ample capacity to ensure that overflowing of contents does not occur. Slurry spreading is usually restricted to defined times of the year when ground conditions are suitable for slurry tankers and when the risk of run-off is low. An interval of two months should elapse between the application of slurry to pasture and the commencement of grazing. Straw used for bedding animals or litter from poultry houses should be composted for at least two months before spreading on land used for tillage.
Control measures for rodents and insects should form part of a biosecurity programme. Rats and mice are often attracted to farm buildings because they provide shelter in cold weather and because of the abundance of food available in such buildings. Rodents can act as reservoirs of Salmonella species which they excrete in their faeces. Rats sometimes shed leptospires in their urine and can transmit these virulent pathogens to domestic animals and to humans. To lessen their attraction for rodents, feed bins should be rodent proof and feed spillages should be cleared up promptly. Strategic use of rodenticides in the vicinity of farm buildings is an effective method for controlling rodent populations.
At the end of a production cycle or following an outbreak of disease, cleaning and disinfection is an essential component of a biosecurity programme. If carried out in a competent manner, cleaning alone can reduce substantially the number of pathogens on building surfaces, thereby decreasing the risk of infection to animals introduced into the building. One of the principal reasons for failure of a disinfection procedure is the presence of residual organic matter on surfaces, equipment or transport vehicles due to inadequate cleaning. Food receptacles and drinkers require special attention in this respect. Selection of an effective and economical disinfectant for the terminal disinfection of a farm building requires consideration of the infectious agents likely to be present, the amount of organic matter remaining on surfaces and the antimicrobial spectrum of the compound selected.
Schemes for the diagnosis, control and prevention of important endemic diseases of animals are formulated by national governments and implemented by veterinary personnel at district level and at farm level. In the event of an outbreak of infectious disease subject to government control, a rigorous testing policy, followed by slaughter of infected animals, segregation, monitoring and retesting of in-contact animals usually applies.
A closed herd or a closed flock is the most effective method for excluding infectious agents from an animal population.
Implementation of a biosecurity programme is dependent on many factors including the size, location and type of farm and the financial resources of the owner. Strategies appropriate for the implementation of a biosecurity programme on a particular farm require a detailed understanding of the enterprise, a positively motivated owner and a realistic estimate of the costs and the likely financial benefits deriving from strict adherence to the measures proposed. In some circumstances, however, biosecurity measures have defined limitations. Close interaction between grazing animals and wildlife can result in the transfer of infectious agents from wild animals to domestic animals. Feral carnivores with rabies can transmit rabies virus not only to domestic animals but also to humans. In these instances, biosecurity measures may be initiated by individual animal owners but ultimately require national government resources for their effective implementation.