The advent of the Final Rule on prevention of SE has created a new awareness of the role of rodents and especially mice in the dissemination of SE within in-line complexes and perpetuation of infection on farms and in houses.

An article on controlling rodents appeared in the November 2008 edition of Egg Industry and serves as a reference to the biology of the three species of rodents which may be found in laying houses. Mice are regarded as the most important reservoir of SE and it is essential that programs should be implemented to suppress population to the point of eradication both in poultry houses and in feed mills.


Control and suppression of rodents requires a coordinated approach involving exclusion, baiting and monitoring. In the words of one prominent U.S. producer, it is necessary to “build rodents out”. Shoddy construction, deterioration of wooden and metal doors, corrosion of cladding, and damage which accumulates over the years provides for easy entry for rodents. Holes as small as a half-inch in diameter can allow entry of mice which seek warmth, feed and shelter especially in late fall or when houses are depleted resulting in migration to adjoining units. A number of producers have initiated programs of patching, replacing and reinforcing corroded metal doors and to ensure a solid seal.

Baiting is a complex issue and professional direction should be obtained from either a consultant or a contractor. The selection of anticoagulant and other chemical rodenticides should incorporate safety, rotation to avoid resistance, placement of bait stations and maintenance of the approved re-baiting process. It is necessary to strictly follow statutory label directions with regard to use, application and disposal of rodenticides.

Deviation from label instructions represents a federal offense and misuse can create issues of liability. Approved rodenticides are classified according to either first- or second-generation anticoagulants or non-anticoagulant compounds as indicated in the table depicting availability of products on the U.S. market. 

Commercially available U.S. rodenticides 

Monitoring requires a system of recording mice caught in curiosity traps, which are placed at strategic points in a house or feed mill as advised by a pest control professional.

The cost of a program should be carefully monitored, but it is emphasized that in the absence of effective control, the entire complex or farm is vulnerable to perpetuation of SE infection following introduction into the operation.   


Classification of rodenticides 

  • First-generation anticoagulants require multiple feeding over several days to produce death. This presumes constant access to bait station.
  • Second-generation anticoagulants generally produce death after a single feeding although there is a cumulative affect over successive days.
  • The non-anticoagulant rodenticides include:
    • Bromenthalin which is a central nervous system toxin;
    • Cholecalcirferol, (Vitamin D3) at a high dose results in mobilization of calcium from bones, increase absorption from the intestinal tract and death from hypercalcemia; and
    • Zinc phosphide, which is subject to strict state controls. The compound releases phosphine in the anterior intestinal tract following ingestion, resulting in acute death.

Although resistance to rodenticides is frequently implicated as cause for ineffective control, this phenomenon is rare, especially with appropriate rotation of compounds. Failure of a rodent control program usually involves insufficient bait stations, neglect of cleaning and re-baiting of stations or other managerial problems, including spillage of feed and providing harborage for mice both inside and outside buildings.

Feed mills 

It is necessary to pay special attention to feed mills as colonization of the unit can result in contamination of feed as apparently determined by FDA inspectors in the current Iowa outbreak. The following precautions should be followed:

  • Sealing the mill against entry of rodents
  • Removal of foliage, scrap and surplus equipment in the vicinity of the mill which provides habitat for survival and breeding
  • Removal of surplus equipment spare parts and tools from floor areas and relocation on racks or hooks to create a clean floor area especially adjacent to walls
  • Bait stations should be placed around the exterior of the mill.
  • Either 2 ft. wide concrete aprons should be constructed or placement of one inch diameter crush stone over a width of 2 ft. will be required to prevent burrowing and entry to the mill.
  • Curiosity traps should be placed on either side of any doorway or entry into the mill.
  • A program should be implemented to remove any spilled feed ingredients or feed in the vicinity of the uploading or dispatch areas and in the vicinity of silos. The availability of seed and feed reduces the effectiveness of bait stations and may also attract wild birds and insects which are equally undesirable.
  • A mill employee should be designated as the person responsible for maintaining or coordinating the cleanliness of the facility, servicing and re-baiting of stations, recording the number of mice caught in curiosity traps and examination for rodent droppings.

Control in houses 

  • Bait stations should be located at 50 ft. intervals around the perimeter of houses and adjacent to egg collection corridors.
  • Bait stations containing the selected rodenticide should be placed in approved bait stations along the outer aisles adjacent to the long walls and if necessary in internal aisles in addition to the work areas at either end of the house.
  • In the event of mouse infestation it is necessary to place wax blocks containing a rodenticide on nails at approximately 30 ft. intervals staggered on either side of the aisle under the bottom feed trough and on ledges.
  • When attempting to suppress brown (roof) rats it is necessary to bait cross-beams and in the event of an attic, both liquid and solid bait should be placed both in the center and adjacent to the eaves on top of the ceiling.
  • Management of manure should include at least annual removal from high-rise houses. Ventilation should allow for drying of the rows so that there is clear access along the entire length of the house to permit placement of bait stations especially adjacent to vertical support beams. It is virtually impossible to eliminate mice from high-rise houses without intensive baiting with appropriate rodenticides following a program of rotation.
  • The presence of rat or mice droppings on egg belts before egg collection is evidence of severe infestation denoting a deficient program. Finding mice or rat droppings on belts will be viewed with disfavor by FDA personnel and may result in sanctions or more intensive and intrusive inspections involving both records and facilities.
  • Storage areas, plant rooms and workshops should be subjected to the same precautions as feed mills and poultry houses.  


Effective control of rodents can no longer be ignored or relegated to a token activity. It is necessary for producers to develop written programs which conform to acceptable standards, planning and implementation. Records will be reviewed by FDA personnel and should quantify rodents captured in curiosity traps, purchases of rodenticides and standard operating procedures for placement, inspection and re-baiting of stations.

Effective rodent control is a vital component of an SE prevention program and should be regarded as being on a level with vaccination and biosecurity as preventive measures.