Biosecurity Tips:

Rodent Monitoring and Control

September, 2000

Why should I worry about

rodent monitoring and control?

Rodents contribute to the introduction and spread of diseases in livestock and poultry production facilities. Rodents, especially rats and mice, can spread diseases within a facility or from an infected facility to neighboring facilities. They can also infect incoming animals.

Rodents also contribute to feed losses and facility damage. A single rat can eat 20 to 40 pounds of feed per year and contaminate up to 300 pounds of feed with its feces and urine. Rodent infestations cost agriculture $1 to 3 billion each year in feed losses alone. Rats and mice will also gnaw on concrete, glass, metal, wood, and electrical wires, causing facility damage.

Research on one poultry ranch chronically infected with Salmonella enteritidis revealed that most of the mice were carriers of the bacteria. Salmonella enteritidis was also found in mouse fetal tissue, showing that the disease can be transmitted from parent to offspring. Droppings from mice on this ranch were able to infect three-week-old chicks.

Diseases spread by rodents:
  • Salmonella enteritidis
  • Encephalomyocarditis
  • Foot and mouth disease
  • Bordetellosis
  • Leptospirosis
  • Swine dysentery
  • Transmissible gastroenteritis
  • Swine erysipelas
  • Toxoplasmosis
  • Trichinosis
  • Ectoparasites – mites and lice

So what can you do to protect your facility from rodent infestation?

  • Know where the rodents are (monitoring).
  • Make your facility less appealing.
  • Restrict rodent access to food and water.
  • Eliminate rodent entry sites to your facility.
  • Institute an elimination program.

Monitoring

Inspect your facility regularly for signs of rodent infestation. These include live rodents and rodent carcasses, gnaw marks, droppings, and burrows. Keep records of where these were observed in your facility. Some companies offer software programs that enable you to input this data, as well as your facility’s floor plan, to better identify the problem areas in your facility.

Most common rats and mice:

  • Norway rat
  • Roof rat
  • House mouse

Facility Improvements

Rodents need three things to survive: food, water, and shelter. Restricting access to these essentials may make them move to another location. This may minimize the need for elimination using traps or poisons.

First, if possible, don’t allow rodents into the buildings where your animals and food are housed. Rodents can enter buildings through holes as small as ¼ inch. Be sure that doors to the facility fit tightly, screen ventilation openings, and inspect the outside of your building for small holes around the foundation. Plug up any potential rodent entry sites.

Second, reduce rodent access to water around your facility. Fix leaky spigots and faucets and fill in any low-lying areas on your property that regularly accumulate water.

Third, rodents find shelter in places with ample cover (tall grasses, piles of trash, under equipment or buildings). Cut down weeds and tall grass around your buildings. Store scrap and trash away from your buildings in covered containers or sealed bins. Don’t give the rodents a place to hide!

Rodent Elimination

Facility improvements and restricting or minimizing rodent access to food and water may control rodent levels. However, if these measures are not successful, elimination of the rodents may be necessary.

Rodent elimination usually comes in two forms: traps and poisons. Traps may be humane (non-lethal) or lethal. Release sites for rodents caught in humane traps should be far enough from the facility to prevent the rodent from returning.

Most traps require baits, which may attract pets or young children. If using bait, use a covered trap accessible only to rodents. Rodents are not attracted to traps with spoiled or low-quality foods. Baits that are similar to the foods rodents are used to eating are best. To determine which bait rodents are most likely to eat, place a small amount of several non-toxic baits one foot apart in several locations where rodent activity was noticed, and check the baits regularly.

Once you determine which baits the rodents prefer, you can mix those baits with rodenticides, or rodent poisons. When using rodenticides, precisely follow the manufacturer’s directions and only use bait that has been approved by the Environmental Protection Agency (EPA). The use of chemical rodenticides is most effective in conjunction with the environmental controls previously discussed.

Rodenticides are available in many forms, including powder, loose meal, pellets, wax, and extruded blocks (large pellets). Rodents less commonly accept wax and blocks, and may find loose meal and pellets more palatable.

Multiple feed anticoagulants

Warfarin (Final®)

Pindone (Pival®, Pivalyn®)

Chlorophacinone (RoZol®)

Diphacinone (Ramik®, Ditrac®)

Single-feed anticoagulants

Brodifacoum (Talon®, Havoc®)

Bromadiolone (Maki®, Contrac®)

Other rodenticides

Bromethalin (Assault®, Vengeance ®, Trounce ®)

Cholecalciferol (Vitamin D3, Quintox®, Rampage®)

Zinc phosphide

Rodenticides are classified into two groups: anticoagulants and other compounds, also called non-anticoagulants.

Anticoagulants prevent blood from clotting and damage the blood vessels, causing the rodent to die of internal bleeding. They are slow acting, which reduces the ability of the rodent to associate the bait with poison and allows time to administer the antidote to animals or people who accidentally ingest the bait.

Anticoagulants can be classified into two categories: multiple feed and single feed. Multiple feed anticoagulants require multiple feedings over several days to produce death. Single feed anticoagulants can result in death after a single feeding, if a sufficient amount of bait was ingested.

Other rodenticides are useful for rapid reductions in the rodent population. Bromethalin causes central nervous depression and paralysis. Cholecalciferol breaks down bone and causes high blood levels of calcium, which disrupts body functions. Zinc phosphide causes convulsions, paralysis, coma, and death.

Reasons for rodenticide failure:

  • Too short a period of bait exposure
  • Insufficient bait
  • Too few bait stations
  • Too small a control area
  • Poor bait choice
  • Improperly placed bait stations
  • Access to other food sources
  • Unappealing bait

Environmental measures and the use of rodenticides should be monitored for effectiveness. Track the location and number of dead rodents seen on the property or the number caught in traps. Analyze changes over time to determine the success of your program.

Cats

Cats are not an alternative to a rodent control program. They are not effective against heavy infestations of mice and may not attack rats. They may also become a reservoir for diseases and spread diseases from the rodents to your animals. Barn cats have been shown to infect swine with the parasitic infection toxoplasmosis.

For more information on rodent monitoring and control, contact your county agricultural commissioner or county cooperative extension agent.

Developed by HJ Hamlen for the California Department of Food and Agriculture, Animal Health Branch, Emergency Programs, 1220 N Street, Room A-107, Sacramento, CA 95814.