How to Control Rodents

Rats and mice have long been a problem on farms where food and nesting sites are plentiful. These animals consume and contaminate food destined for livestock and other animals, as well as humans. Each rat on a farm will eat, spoil or damage approximately N9,000 worth of grain per year. The adaptability and agility of these animals make getting rid of them particularly difficult. Mice are capable of running up a vertical surface, negotiating a wire like the finest circus performer and can easily jump to a height of 30 cm (12 in.) from a flat surface.

Why Control Rodents?

Damage comes in many forms:

  • Damage to buildings. Mice and rats will damage wood and electrical wiring, which can be a fire hazard.
  • Destruction of insulation. Many livestock and poultry facilities show serious deterioration within 5 years. Associated with this damage are costs for re-insulation, increased energy costs and poorer feed conversions by animals.
  • Feed consumed. A colony of 100 rats will consume over 1 tonne of feed in 1 year.
  • Feed contaminated. A rat can contaminate ten times the amount of feed it eats with its droppings, urine and hair. A rat produces 25,000 droppings per year, a mouse 17,000.
  • Biosecurity. Rodents are recognized as carriers of at least 45 diseases, including salmonellosis, pasteurellosis, leptospirosis, swine dysentery, trichinosis, toxoplasmosis and rabies. Mice and rats can carry disease-causing organisms on their feet, increasing the spread of disease.

Understanding Rodents

Mice and rats have tremendous breeding potential. One female mouse can give birth to 5-10 litters per year, yielding five to six young per litter. The gestation period is a mere 19-21 days. These babies are sexually mature in 6-10 weeks. The average female mouse lives to 9 months of age.

Under ideal situations, a pair of rats and their offspring can produce 20,000,000 young in 3 years. One female rat is capable of producing another 22 breeding females in 1 year (assuming a 50:50 male/female ratio of offspring), which mature within 3 months.

Rats and mice have poor eyesight but excellent senses of smell, taste, touch and hearing. They do not like open areas and prefer contact with walls and other objects. They do not range far from the nest. The range for rats is up to 45 m (148 ft), for mice 9 m (30 ft). Rats are extremely apprehensive about new objects and will avoid them for several days. Leaving a trap or bait station out for about 5 days is necessary to ensure acceptance. Mice quickly accept new objects. These tendencies become very important when designing baiting or trapping programs.

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Poultry farmers/Producers should not be embarrassed to admit they have a rodent problem. The embarrassment and costs occur if something is not done to confront the problem.

Monitoring your pens is an important step in preventing and/or controlling rodent populations. Traditional rodent control methods such as baiting and trapping can also be used as a monitoring tool. Thorough record-keeping of bait disappearance can warn farmers if their rodent population is increasing. This is especially important in the fall, when rodents start to look for suitable wintering sites. Be aware that bait can become stale and mouldy, and must be refreshed often to prevent bait aversion and maintain the effectiveness of your monitoring program.

The following are signs of rodent infestation:

  • Sounds: Gnawing, climbing noises in walls, squeaks.
  • Droppings: Found along walls, behind objects and near food supplies.
  • Burrows: Rat burrows are indicated by fresh diggings along foundations, through floorboards into wall spaces.
  • Runs: Look for dust-free areas along walls and behind storage material.
  • Gnawing marks: Look for wood chips around boards, bins and crates. Fresh gnawing marks will be pale in colour.
  • Rodent odours: Persistent musky odours are a positive sign of infestation.
  • Visual sighting: Daylight sighting of mice is common. Rats are seen in daylight only if populations are high. Quietly enter your barn at night, wait in silence for 5 minutes and listen for the sound of rodent activity. Look around with a powerful flashlight; rat eyes will reflect the light.
  • Smudge marks: These may be found on pipes or rafters where dirt and oil from their fur leave a greasy film.

It is a generally accepted rule of thumb that there are approximately 25 mice or rats for every one that is seen. If you see rats and mice during daylight hours, it may indicate a severe infestation, as the population and feeding pressures are so high that juveniles are forced to forage during the day.

Rodent Control (The Principles)

Rodent control requires an integrated pest-management strategy involving many techniques. The poultry farmer/producer’s first objective should be to prevent, or at least greatly reduce, rodent numbers through management programs that eliminate entrance to the facility, nesting sites for the rodents, food supplies and water. Populations build when food, water and nesting sites are readily available.

Rodent-Proofing Farm Buildings

Proper construction and maintenance of buildings helps prevent rodents from entering your barn. Initial construction footings should extend 0.5 m (19 in.) into the ground, with an apron that extends 0.2 m (8 in.) outward. This prevents rodents from burrowing into your building. To prevent frost damage, footings may have to be deeper. Examine your building at least once a year for possible entryways for rodents. Remember, a mouse needs only a 0.6 cm (1/4 in.) opening to gain access; rats need a 1 cm (1/2 in.) opening. As a general guideline, mice can enter an enclosure through a hole the size of your little finger, and rats through a hole the size of your thumb. Cracks around door frames, under doors, broken windows, water and utility hook-ups, vents and holes surrounding feed augers are potential points of entry. Use coarse steel wool, hardware cloth or sheet metal to cover/fill any entrances. Do not use plastic, wood or insulation, as rodents simply gnaw their way through.

When constructing walls, ensure that sheeting lies flush to the wall studs rather than on strapping. This keeps nesting sites confined to a single section between studs rather than allowing complete access to all wall spaces.

A well-maintained structure is your first defence against rodents. Most rodents enter your pen/barn directly from the fields and then the population builds. It is important to maintain good sanitation outside the pen/barn. Eliminate vegetation 1 m (3 ft) around buildings and replace with crushed rock as rodents cannot tunnel through this material. Clean up spilled feed, remove loose wood, garbage, etc. Do not attract rodents from fields to your operation.

Eliminating Hiding Places and Nesting Sites

Rodents do not like to be exposed. Maintain sound housekeeping, eliminate loosely piled building materials, old feed bags, trash or anything else that a rodent can hide in or under. Keep piles of lumber and miscellaneous equipment 24-30 cm (9-12 in.) off the floor and at least 24 cm (9 in.) out from a wall. Look for entrances into double wall construction. Most rodents nest in the insulation of double walls. Block off all entrances into walls and destroy all nesting material.

Remove Food and Water

Eliminate water sources such as leaky taps, open water troughs, sweating pipes and open drains. Keep all feeds in rodent-proof bins, covered cans or metal hoppers. Reduce feed spillage and immediately dispose of dead animals. Without readily available food and water, populations cannot build.

Control of Existing Population

If there is already a rodent problem inside the barns, prevention alone won’t solve the problem. In this case, consider a population-reduction program.

Snap Traps

For small populations, snap traps or box traps are very useful for eliminating rodents. Rats prefer fresh bacon, fish and meat, while mice favour cheese, peanut butter or seeds. Try several baits to find out which your rodents prefer. Rats are distrustful of anything new in their environment, so leave baited non-set traps out for 4-5 days to allow them to get used to the traps. Ensure that previous baits have been taken before actually setting the traps. If rats are the problem, use rat traps. If mice are the problem, use a mouse trap. Locate traps close to walls, behind objects, in dark corners, where you see droppings or gnaw marks. When trapping next to a wall, set the trap at right angles to the wall with the trigger and bait closest to the wall. Orient multiple-catch traps with the entrance hole parallel to the wall. Live traps can work very well near runways used by mice and rats.

Glue Boards

Glue boards are very effective against mice and are the method of choice in locations where toxic baits are a concern. Glue boards will not work well if there is too much dust. Check glue boards and traps daily and remove and dispose of dead mice and rats. Abundant food supplies make baited traps less effective. Eliminate as many sources of food as possible before starting a program. For barns and poultry houses with moderate infestations, set 50-100 traps. The trapping program should be short and decisive to prevent trap shyness.

Wear rubber gloves when handling bait, bait stations, traps or dead rodents to prevent human scent transfer, accidental poisoning or disease transmission. Place the rodents in tightly sealed plastic bags.

Predators

Cats may limit low-level mouse or rat populations. However, if conditions are ideal for rodents, cats cannot eliminate a problem. Cats may introduce disease into a facility by bringing in rodents caught in fields. Cats will not be able to catch mice as quickly as they multiply.

Conclusion

Elimination of rats and mice from livestock and poultry barns is extremely difficult. It is preferable for producers to prevent infestations from occurring. If a problem does exist, the options described in this Factsheet should be useful in limiting rat and mice populations. If problems persist, farmers may find advice from professional pest control personnel helpful. These professionals can assist with identifying entry/nesting sites. They can also provide advice on placement of bait stations, traps, baiting and bait monitoring.

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