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Establish robust rodent control to advance biosecurity

By MWI Animal Health

Removing rodents from facilities helps mitigate the exposure of poultry to disease
rodent control bait stations

Rodents and insects are considered mechanical vectors of disease in poultry houses. They carry bacteria, fungi, protozoa, viruses, and parasitic worms on the interior and exterior of their bodies and transfer these pathogens between hosts when they are consumed or when they contaminate food and water sources.

One way that we can mitigate the exposure of poultry to disease is to remove vectors from the equation, and this includes rodents.

Rodents, namely mice and rats, are physically destructive to infrastructure such as foundations, walls, electrical wiring, and insulation, and cause considerable feed loss. They have been implicated as vectors of over 35 pathogens including Salmonella sp., Campylobacter sp., Cholera, Leptospirosis, Bordetellosis, Hanta virus, LCMV (Lymphocytic chroniomeningitis virus)1 and possibly even avian influenza.2

Rodents are attracted to animal production because houses provide them with shelter, an abundance of food, and a perfect climate for reproduction and development. 

The 6 pillars of a rodent control program

  1. Set up bait stations around the perimeter of the interior and exterior of poultry houses
  2. Keep them replenished with fresh bait
  3. Monitor for activity using live traps, snap traps, sticky traps, or new sensing technology
  4. Rotate between active ingredients and modes of action
  5. Be familiar with rodenticide formulations or ‘matrices’
  6. Carry out baiting methods with respective matrices in tamper-proof bait boxes, inside of barns, at barn cleanout, in burrows, and for difficult-to-reach places
1. Place tamper-proof bait stations around perimeters

In an attempt to prevent rodents from migrating from nearby vegetation and buildings, place tamper-proof bait stations against exterior walls of houses.

It is recommended that stations be placed every 30–50 feet for rats. Stations targeting mice should be placed every 10– 15 feet, based on the average maximum foraging distances for each species.

For new construction, these exterior bait stations may suffice until rodents are detected on the interior of houses. At that point, rodent bait stations need added to the perimeter of interior walls using the same spacing as described for each species.

Tamper-proof bait stations can even be deployed around debris piles, fence lines, and the edges of woods as an added line of defense further from houses. Advances in bait station technology include the additions of weights (Tomcat® Titan and Aegis-RP Anchor) to keep stations from being moved away from their intended location (i.e. up against walls where rodents like to travel). Also, some stations are designed to be mounted vertically (Tomcat® Vertical and Aegis® Bait Stations) to keep them in place and out of the way of mowers and workers.

2. Clean and replenish bait boxes — don’t set and forget!

The number one reason rodenticide programs fail is that bait boxes are not cleaned and replenished often enough. To improve the effectiveness of a program, check bait boxes at least once a month. Make sure they’re not empty and the bait isn’t moldy or stale.

If bait is old, totally replace it. If the bait is totally consumed, it needs replenished with fresh bait. Remember: The frequency of bait box maintenance should increase with increased rodent pressure.

3. Monitor for rodent activity with traps

Monitoring for rodent activity helps discover where rodents are nesting and foraging and gives insight into their population density.

What to look for:

  • Anything larger than dime-sized holes in walls. Seal up as many as you can using sturdy materials such as concrete, steel, or galvanized sheet metal.
  • Rub marks along walls and pillars where oil and dirt from rodent bodies have left behind a dark, shiny trail.

Use these holes and rub marks as indicators of where to focus your baiting strategies. Place sticky traps, snap traps, or live traps along walls in places where rodents are suspected to travel. The number of rodents caught in these traps should serve as data points that can be used to measure changes over time in population densities as new strategies are added to your rodent program or new baits are evaluated. Dispose of, reset, and/or replace these traps as needed when they are full. If no rodents are detected within a week, move the traps to another location. 

4. Understand rodenticide classes and rotate between active ingredients and modes of action

When it comes to rodenticide classes, there are only three: neurotoxins, anticoagulants, and hypercalcaemics.

Neurotoxins. Neurotoxins affect the central nervous system, causing paralysis, and include the active ingredients bromethalin and zinc phosphide. Neurotoxins tend to achieve the fastest mortality of rodents of the three classes (usually within hours to a couple of days depending on the formulation). Unfortunately, this can lead to bait shyness, or avoidance of bait. For this reason, neurotoxins can often only be used for a few weeks at a time.

Anticoagulants. Anticoagulants prevent the liver from producing vitamin K, which leads to internal bleeding. Anticoagulant active ingredients include brodifacoum, bromadiolone, difethialone, difenacoum, and diphacinone. You can expect anticoagulants to affect rodents that receive a lethal dose within 3–8 days.

Cholecalciferol. Cholecalciferol is vitamin D3 and is the only hypercalcaemic used in rodent control. An overdose of this vitamin delivered through rodent bait causes excessive calcium buildup in the blood stream. This leads to muscle weakness and calcification of blood vessels, heart valves, liver, kidneys, and other soft tissues. This eventually leads to death.3 This active ingredient typically requires multiple feedings to achieve a lethal dose and causes death within 4–6 days.

The most important aspect to remember about rodenticide classes is this:

It is imperative to periodically rotate between classes in order to avoid resistance. Rodenticide resistance in rodents to first- and second-generation anticoagulants has been found in several European countries.4 Rotate between active ingredients every 4–6 months and utilize at least two rodenticide classes each year.

5. Be familiar with rodenticide formulations or ‘matrices’

Rodenticide active ingredients are presented in many inactive ingredient formulations called matrices. These include blocks or chunks, soft baits, meal baits, pellets, pitch packs, powders, and liquids.

6. Carry out baiting methods with respective matrices 

Each matrice has its own uses and advantages:

  • For tamper-proof bait boxesBlocks or chunks are typically used in tamper-proof bait boxes. They have a hole drilled through the middle to skewer them on rods inside bait boxes in order to keep them secure and in place.
  • For inside of housesSoft baits can also be placed on skewers in bait boxes but are also often skewered on wire or nails and placed inside of houses where non-target animals do not have access to them. The soft baits tend to be highly palatable.
  • For barn cleanout — An ideal opportunity for rodent control is when animals are removed from houses for cleanout. There are no non-target animals present that require all bait to be in bait stations, so this is an ideal time to utilize neurotoxins. Meal bait and pellets are often used in trays, such as egg flats or paper plates, on the interior of barns when animals are removed. Place the flats of meal bait 10–15 feet for mice and 30–50 feet for rats as described for bait boxes. No more than a cup of bait should be used in each tray and replenish the bait as it is consumed. Overloading the trays with bait can lead to waste. Pick up all meal bait or pellet trays before animals are reintroduced into houses.
  • For burrow baitingMeal baits or pellets should also be placed deep in rodent burrows. Burrows can be found in the soil near the exterior foundation and in manure piles in pits. Cover each burrow with your foot or shovel. Any new burrows that are uncovered within a few days should be baited. The simplest method of burrow baiting is to attach a funnel to a 4-foot long piece of ½-inch PVC pipe. Insert the end of the pipe 6 inches down into the burrow and apply 1 tablespoon of bait into each burrow. Re-cover each baited burrow with soil. 
  • For difficult-to-reach areasPitch packs are intended for use in areas that are difficult to reach. They act as miniature bait stations in wall voids and attics. They are filled with anticoagulant bait as either meal bait or pellets. A newer invention in attic baiting is Neogen® Attic Attack Bait Stations. These 3-inch round bait stations can be inserted into pre-drilled holes in ceilings and allow you to bait, from below, hard-to-access attics. Once the traps are in place, you can remove the insert, place bait on a skewer, and replace the insert back into the station. Once the bait is consumed, a red indicator flag pops out to let you know which stations need serviced.

In summary

Removing mechanical vectors of disease helps protect our animals, farms, and food supply, much the same as rodenticide technologies and a robust rodent control program can advance a facility’s biosecurity.  

There’s an app for that: Remote sensing technology monitors bait stations

Motomoco iQ™ is a newer remote sensing technology that records the number of rodent “hits” on a bait station. Special sensing trays can be placed in the bottom of Tomcat® Titan, Bullet, Live Catch, or Rat Traps. Each time a rodent enters a bait station, the sensor records that data point as an event. The station automatically sends this recorded data to an app downloaded on an individual’s cell phone or tablet whenever they get within several feet of the station. The app software will then generate a report that shows which traps have been most frequented.

This information helps make decisions on which traps need to be serviced and the location of the highest rodent activity. Over time, this data should prove invaluable for determining the effectiveness of rodent control programs and may provide an indication of how dedicated employees are to rodent control.

1Loncke, T. and Dewulf, J., 2019. Rodent Control in Animal Production. Biosecurity in Animal Production and Veterinary Medicine, p.283.
2Velkers, F.C., S.J. Blokhuis, E.J.B. Veldhuis Kroeze, and S.A. Burt. 2017. The role of rodents in avian influenza outbreaks in poultry farms: a review. Veterinary Quarterly 37: 182–194.
3Rumbeiha, W.K. 2006. Cholecalciferol. Small Animal Toxicology, 2nd ed.; Peterson, M.E.; Talcott, P.A., Eds.; Elsevier Saunders: St. Louis, MO; pp 629–642.
4Meerburg, B.G., M.P. van Gent-Pelzer, B. Schoelitsz, and T.A. van der Lee. 2014. Distribution of anticoagulant rodenticide resistance in Rattus norvegicus in the Netherlands according to Vkorc1 mutations. Pest Management Science 70: 1761–1766.