Elimination of rats and mice from livestock and poultry barns is extremely difficult. Most of the time they reproduce faster than you can eliminate them. Therefore it is preferable for producers to prevent infestations from occurring.
By Wiebe van der Sluis
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 €20 worth of grain per year, says Brian Lang of the Ontario Ministry of Agriculture, Food andRural Affairs (OMAFRA). He studied the rodent problem and wrote an interesting paper on it. In the following we take with permission a closer look at some of his findings and advice for control.
Why control rodents?
The adaptability and agility of rodents make getting rid of them particularly difficult and 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 facilities show serious deterioration within five years, resulting in increased energy costs, re-insulation costs and poorer feed conversions by animals.
• Feed consumed- 100 rats will consume over one tonne of feed in one year.
• Feed contaminated- A rat can contaminate 10 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 recognised as carriers of approximately 45 diseases, including salmonellosis, pasteurellosis, leptospirosis, swine dysentery, trichinosis, toxoplasmosis and rabies.
Mice and rats have tremendous breeding potential. Under ideal situations, a pair of rats and their offspring can produce 20 million young in three years. Mice reproduce even faster. One female mouse can give birth to five to 10 litters per year, yielding five to six young per litter. The gestation period is a mere 19 to 21 days. These babies are sexually mature in six to 10 weeks. The average female mouse lives to be nine months. One female rat is capable of producing another 22 breeding females in a year (assuming a 50:50 male/female ratio of offspring), which mature in three months after parturition.
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 maximum range for rats is 45 metres (148 feet), for mice nine metres (30 feet). Rats are extremely apprehensive about new objects and will avoid them for several days. Leaving a trap out for about five days is necessary to ensure acceptance. Mice quickly accept new objects. These tendencies become very important when designing baiting or trapping programmes.
Is it a rat or a mouse problem?
Since rats and mice require different control strategies, therefore determine whether the problem is rats or mice (Table 1
). The simplest way to differentiate between the types of infestation is by examining the droppings. Mouse droppings are black and rice-kernel size, whereas rat droppings are black and bean-sized. Rats and mice are considered to be omnivorous.
Given a choice, they prefer cereal grains. However, when food supplies are scarce, they will eat almost anything. Rats and mice eat every day. Rats usually drink every day, but mice can survive several days without water.
Rodent control principles
Rodent control requires an integrated pest-management strategy involving many techniques. The producer’s first objective should be to prevent, or at least greatly reduce, rodent numbers through management programmes that eliminate entrance to the facility, nesting sites for the rodents, food supplies and water.
To control mice and rats, we have to understand their habits and biology first. Mice and rats are similar in their habits and biology, although there are some differences between the two:
• Both are highly reproductive and extremely capable of surviving in all kinds of conditions.
• On farms, mice and rats will be near a food source such as barns, granaries, livestock buildings and silos.
• Rats and mice can climb and jump. Rats can jump vertically as high as 91 cm and horizontally as far as 122 cm.
• Mice and rats can climb brick and other rough walls, and travel along utility wires.
• Rats can cross (sneak in) through openings as small as 1 cm and mice can squeeze through openings of 0.6 cm, or less, in diameter.
• Both mice and rats are active at night, particularly right after dusk.• Rats are smart and tend to avoid new objects. Therefore, it may take a few days for traps and baits to work.
Rodent-proofing farm buildings
Proper construction and maintenance of buildings helps prevent rodents from entering your barn. Examine your building at least once a year for possible entry ways for rodents. Cracks around door frames, under doors, broken windows, water and utility hook-ups, vents and holes surrounding feed augers are all potential points of entry. Use coarse steel wool, hardware cloth or sheet metal to cover any entrances. Do not use plastic, wood or insulation, as rodents simply gnaw their way through.
A well maintained structure is the first defence against rodents. Most rodents enter the barn directly from the fields, then the population builds. It is also important to maintain good sanitation outside the barn to not attract rodents. Eliminate vegetation for one metre (three feet) around buildings, clean up spilled feed, remove loose wood, garbage, etc. Rodents do not like to be exposed. Maintain sound housekeeping, eliminate loosely piled building materials, old feed bags or anything else that a rodent can hide in or under. Look for entrances into double wall or roof constructions because most rodents like to nest there in the insulation. Block off all entrances into walls and destroy all nesting material.
Control of existing population
If there is already a rodent problem inside the barns, prevention alone will not solve the problem. In this case, consider a population-reduction programme.
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 four to five days to allow them to get used to the traps. Ensure that previous baits have been taken before actually setting the traps.
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. For barns and poultry houses with moderate infestations, set 50 to 100 traps. The trapping programme should be short and decisive to prevent trap shyness. Odours from humans or previously caught rodents do not cause trap shyness.
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. They are only recommended where dust can be kept away from them. Check glue boards and traps daily and remove and dispose of dead mice and rats. Wear rubber gloves when handling them to prevent any chance of disease infection.
Rodenticides (toxic baits) - There are two basic types of rodenticides: acute poisons and anti-coagulants. Use rodenticides when control of moderate-to-large rodent populations is necessary. Many of the newer anti-coagulant products, i.e. bromadiolone and brodifacoum require single feedings by rodents to cause mortality. Occasionally, rodents may develop a bait shyness after being made sick but not killed by a rodenticide.
The shyness develops to the bait carrier, e.g. grain, and not to the rodenticide. Simply use another formulated product or different attractant if bait shyness develops. For rats, pre-bait using baits without the poison for about one week to get them accustomed to the bait. Place baits in areas of high rodent activity. Many people under-bait in their control programme. Baits should be 1 to 2 metres (3 to 6 feet) apart for mice and 7 to 10 metres (23 to 33 feet) for rats. Remove all uneaten baits and properly dispose of them after the poisoning programme.
When using rodenticides safety measures should be taken. Ideally, cover all baits to prevent consumption by children, cats, dogs and poultry. This can be done by placing baits in bait stations or bait boxes that allow ready access by rodents but prevent larger animals from gaining access.
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 five 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.