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06/03/2009 15:12:06
Salmonella - The importance of rodent control
The threats posed by rodents are generally well known but current concerns regarding the role of rats and mice in the maintenance and spread of salmonella in laying flocks has increased awareness of the important part that rodents play in the spread of this disease.
Project 0Z0325 being undertaken by Defra VLA has identified and confirmed that rodent infestations are usually the most significant factor in salmonella infection, particularly S.Enteritidis (SE) and S.Typhimurium (ST), persisting on farms between flocks. Despite cleaning and disinfection measures taken during turn round periods, infected rats and mice that remain within the structure of the house or are able to regain entry once birds have been introduced, pose long term problems of recycling infection between breeding rodent colonies and birds This is particularly true of free-range production where normal disinfection is usually effective in interrupting the cycle of infection when birds are vaccinated for salmonella and precautions taken to avoid ’walking’ infection between flocks are taken.
Rodents are also more likely to be heavily infected than birds so most of the SE or ST in an infected house comes from rodent faeces which contaminate egg belts and therefore eggs, walkways, beams, ledges and litter or manure. This means that the boot swab samples that free-range producers will take for salmonella monitoring in the future may be positive as a result of rodent contamination of the sample rather than positive faeces from the birds. This does not mean that the birds are not infected or that the rodents can maintain infection for a long time in a house where birds are not infected as both are needed to maintain a cycle of infection – just that infected rodents are more likely to result in high level contamination and a positive monitoring test.
Salmonella carriage in free-living rodents is rare – they pick up salmonella from their environment and harbour it rather than acting as a major source of introduction of new infections on to a farm. If the flocks on a farm are salmonella-negative then the rodents will also be negative. If this is the case the action to eliminate rodents does not need to be so intensive so it is wise to carry out detailed sampling to find out what the salmonella-status of the flocks is. If some houses on a farm are persistently contaminated with salmonella it makes sense to concentrate on rodent control in these first. Eliminating rodents from a salmonella- negative house and not an adjacent infected house may worsen problems if infected rodents move to the previously uninfected house as a result of reduced competition or disturbance during depopulation of the infected house. It is therefore important to control rodents effectively throughout the life of the flock and not leave it until the house is empty.
It is acknowledged that poultry units are difficult situations in which to control and prevent rodent infestations. The availability of palatable feedstuffs, constant favourable environmental conditions and numerous sites in which rats and mice can seek harbourage in areas which protect them from the birds, are all factors that contribute to the problem.
Key considerations and action points for rodent control include:
If effective results are to be achieved, it is important that control measures are included as a high priority, planned part of the enterprise management
Consider if the intensive work required to eliminate established rodent populations can be undertaken by suitably trained farm staff or if the services of a contractor should be used. In many cases daily action is required to reduce severe infestations so it may be more appropriate to use a contractor in conjunction with farm staff who are carrying out most of the baiting and other controls.
Regular inspections of all sections of the unit must be undertaken to check for evidence of rodent infestation. The species, population levels and distribution should be confirmed and action taken accordingly
Detecting rodents can be difficult particularly in low light conditions and in areas where access is restricted. A powerful torch is essential in order to locate fresh droppings, grease marks or footprints in dust, gnawing damage, holes in structures or burrows in manure accumulations and routes regularly used by rats and mice. Smell can help identify the location of rodents but this varies between individuals and a ’mousy’ or ’ratty’ smell is best detected on first entry to the house from the fresh air.
Mice often occupy small territories within buildings whilst rats, in addition to living in structures may be harboured in ditches, hedgerows or other outdoor locations. The aim should be to identify where rodents are living, travelling and feeding
Rats are characteristically cautious animals and will avoid new objects such as bait boxes or materials possibly for several weeks. This has particular relevance where time is limited during which control needs to be achieved. Laying rodenticides as naturally as possible (including placing bait points in voids, making use of existing material on the site and burrow or hole baiting followed by covering the baited holes to protect non-target animals) will help to reduce this problem and encourage rats to feed.
Mice are inquisitive by nature and so using different types of bait boxes or containers and several bait formulations simultaneously can be beneficial. Moving bait points regularly may improve bait consumption.
A flexible approach to the choice of control methods and how these should be applied is necessary. Although there is a limited number of rodenticides approved for use there are a wide range of formulations and products. A majority are available to be used by both competent and trained farm staff and pest contractors. The decision on which product to use is less important than the way the baiting treatment is applied and undertaken and how well it is accepted by the rodents The uptake of different bait formulations varies between farms so it is best to experiment to find out what gives best results on an individual unit.
Particular problems with free-range houses may relate to harbourage of mice at the end of nest box housings, infestation of roof spaces by rodents using the tops of partitions as walkways, colonisation of dry manure on beams of deep or within mini-pits or burrowing of rats from the exterior of the house. Each problem will require a targeted approach to achieve effective control and standard routine programmes are not likely to be successful where rodents have already built up.
Safe use of rodenticides is an important consideration and the information on product labels should be read and the precautions and directions for use followed. Staff using pesticides in the course of rodent control work must be adequately trained and instructed.
Trapping and other physical techniques can play a part in a control programme that often needs to include a range of options and measures but its main role is to help monitor rodent populations. Reducing harbourages and site attraction to rodents by ’good house keeping’ – especially with regards to clearing spilled feed and clutter from outside houses and feed spills from pits. Proofing vulnerable areas such as the base of doors and holes chewed or gnawed in structures, will help to prevent rat and mouse infestations establishing and increasing.
For further advice and information contact:
Paul Butt Wildlife Management & Licensing Team, Natural England, Olantigh Road, Wye Kent TN25 5EJ tele: 01233 811265 email: paul.butt@naturalengland.org.uk
Rob Davies Food & Environmental Safety Department, Veterinary Laboratories Agency, Weybridge, New Haw, Addlestone Surrey KT15 3NB
Tele: 01932 357361 email: r.h.davies@vla.defra.gsi.gov.uk
 | Rat Droppings |
 | Rat Burrow |
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Project 0Z0325 being undertaken by Defra VLA has identified and confirmed that rodent infestations are usually the most significant factor in salmonella infection, particularly S.Enteritidis (SE) and S.Typhimurium (ST), persisting on farms between flocks. Despite cleaning and disinfection measures taken during turn round periods, infected rats and mice that remain within the structure of the house or are able to regain entry once birds have been introduced, pose long term problems of recycling infection between breeding rodent colonies and birds This is particularly true of free-range production where normal disinfection is usually effective in interrupting the cycle of infection when birds are vaccinated for salmonella and precautions taken to avoid ’walking’ infection between flocks are taken.
Rodents are also more likely to be heavily infected than birds so most of the SE or ST in an infected house comes from rodent faeces which contaminate egg belts and therefore eggs, walkways, beams, ledges and litter or manure. This means that the boot swab samples that free-range producers will take for salmonella monitoring in the future may be positive as a result of rodent contamination of the sample rather than positive faeces from the birds. This does not mean that the birds are not infected or that the rodents can maintain infection for a long time in a house where birds are not infected as both are needed to maintain a cycle of infection – just that infected rodents are more likely to result in high level contamination and a positive monitoring test.
Salmonella carriage in free-living rodents is rare – they pick up salmonella from their environment and harbour it rather than acting as a major source of introduction of new infections on to a farm. If the flocks on a farm are salmonella-negative then the rodents will also be negative. If this is the case the action to eliminate rodents does not need to be so intensive so it is wise to carry out detailed sampling to find out what the salmonella-status of the flocks is. If some houses on a farm are persistently contaminated with salmonella it makes sense to concentrate on rodent control in these first. Eliminating rodents from a salmonella- negative house and not an adjacent infected house may worsen problems if infected rodents move to the previously uninfected house as a result of reduced competition or disturbance during depopulation of the infected house. It is therefore important to control rodents effectively throughout the life of the flock and not leave it until the house is empty.
It is acknowledged that poultry units are difficult situations in which to control and prevent rodent infestations. The availability of palatable feedstuffs, constant favourable environmental conditions and numerous sites in which rats and mice can seek harbourage in areas which protect them from the birds, are all factors that contribute to the problem.
Key considerations and action points for rodent control include:
If effective results are to be achieved, it is important that control measures are included as a high priority, planned part of the enterprise management
Consider if the intensive work required to eliminate established rodent populations can be undertaken by suitably trained farm staff or if the services of a contractor should be used. In many cases daily action is required to reduce severe infestations so it may be more appropriate to use a contractor in conjunction with farm staff who are carrying out most of the baiting and other controls.
Regular inspections of all sections of the unit must be undertaken to check for evidence of rodent infestation. The species, population levels and distribution should be confirmed and action taken accordingly
Detecting rodents can be difficult particularly in low light conditions and in areas where access is restricted. A powerful torch is essential in order to locate fresh droppings, grease marks or footprints in dust, gnawing damage, holes in structures or burrows in manure accumulations and routes regularly used by rats and mice. Smell can help identify the location of rodents but this varies between individuals and a ’mousy’ or ’ratty’ smell is best detected on first entry to the house from the fresh air.
Mice often occupy small territories within buildings whilst rats, in addition to living in structures may be harboured in ditches, hedgerows or other outdoor locations. The aim should be to identify where rodents are living, travelling and feeding
Rats are characteristically cautious animals and will avoid new objects such as bait boxes or materials possibly for several weeks. This has particular relevance where time is limited during which control needs to be achieved. Laying rodenticides as naturally as possible (including placing bait points in voids, making use of existing material on the site and burrow or hole baiting followed by covering the baited holes to protect non-target animals) will help to reduce this problem and encourage rats to feed.
Mice are inquisitive by nature and so using different types of bait boxes or containers and several bait formulations simultaneously can be beneficial. Moving bait points regularly may improve bait consumption.
A flexible approach to the choice of control methods and how these should be applied is necessary. Although there is a limited number of rodenticides approved for use there are a wide range of formulations and products. A majority are available to be used by both competent and trained farm staff and pest contractors. The decision on which product to use is less important than the way the baiting treatment is applied and undertaken and how well it is accepted by the rodents The uptake of different bait formulations varies between farms so it is best to experiment to find out what gives best results on an individual unit.
Particular problems with free-range houses may relate to harbourage of mice at the end of nest box housings, infestation of roof spaces by rodents using the tops of partitions as walkways, colonisation of dry manure on beams of deep or within mini-pits or burrowing of rats from the exterior of the house. Each problem will require a targeted approach to achieve effective control and standard routine programmes are not likely to be successful where rodents have already built up.
Safe use of rodenticides is an important consideration and the information on product labels should be read and the precautions and directions for use followed. Staff using pesticides in the course of rodent control work must be adequately trained and instructed.
Trapping and other physical techniques can play a part in a control programme that often needs to include a range of options and measures but its main role is to help monitor rodent populations. Reducing harbourages and site attraction to rodents by ’good house keeping’ – especially with regards to clearing spilled feed and clutter from outside houses and feed spills from pits. Proofing vulnerable areas such as the base of doors and holes chewed or gnawed in structures, will help to prevent rat and mouse infestations establishing and increasing.
For further advice and information contact:
Paul Butt Wildlife Management & Licensing Team, Natural England, Olantigh Road, Wye Kent TN25 5EJ tele: 01233 811265 email: paul.butt@naturalengland.org.uk
Rob Davies Food & Environmental Safety Department, Veterinary Laboratories Agency, Weybridge, New Haw, Addlestone Surrey KT15 3NB
Tele: 01932 357361 email: r.h.davies@vla.defra.gsi.gov.uk
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