Rats and mice can cause significant damage to your farm
/by Heather McLean
Rats and mice are often a problem on farms. In particular, autumn can be when you may see populations noticeably increasing in and around barns as food supplies in the fields disappear and the cold weather sets in.
Rodents might be small but they can cause significant damage to your farm. They can cause damage to insulation, wood, and electrical wiring.
A rat can eat 10 to 20 kilograms of feed in a year, and a pair of mice will eat two kilograms. They can contaminate 10 times the amount of feed they eat with their droppings, urine, and hair. Rodents are recognized carriers of at least 45 diseases, including dysentery, leptospirosis, trichinosis, salmonellosis, toxoplasmosis, and rabies.
UNDERSTANDING RODENTS
A few mice and rats can easily multiply into several hundred within a few months. One female rat can produce six to seven litters of eight to 10 young in a year. Mice can have five to 10 litters of five to six young per year.
Rats and mice have very poor eyesight but excellent senses of smell, taste, touch, and hearing. They don’t like open areas and prefer contact with walls and other objects. They don’t range far from the nest, about 45 metres for rats and nine metres for mice.
Rats are very apprehensive about new objects and will avoid them for several days, whereas mice quickly accept new objects. Both are more active at night, particularly right after dusk.
Rats and mice prefer cereal grains (and rats eat meat when available), but they will eat almost anything when food is scarce. They both eat every day, and while rats prefer access to water daily, mice can survive several days without water.
Rats can squeeze through holes as small as one centimetre (0.5 inch) and mice can fit through holes as small as 0.6 cm (0.25 inch).
EVALUATING POPULATIONS
There are several indicators of a rodent population on a farm:
• Sightings: rodents are nocturnal, so not seeing any doesn’t mean they aren’t there. Daylight sightings of mice are more common. Rats are only seen during the day if populations are high. Quietly enter the barn at night and wait five minutes. Look around with a flashlight. Rodent eyes will reflect the light.
• Sounds: by standing quietly in the barn, you may hear gnawing, climbing sounds in walls, or squeaks.
• Droppings: fresh droppings of rats are black and about 1.9 cm (0.75 inch) long, while mouse droppings are black and 0.6 cm (0.25 inch) long.
• Other signs: look for runways, tracks, and rub marks where rodents have travelled. Look for gnaw marks or wood bits around boards, bins, and crates. There may also be signs of burrows in the ground or nests.
PREVENTION SUGGESTIONS
Construct buildings in a manner that discourages rodents from entering. Doors should fit tightly, with metal kick plates and no gaps.
Drain cover holes should be less than 0.6 millimetres in size.
Seal any openings, including those around windows, doors, and vents, and where utilities, conduits, pipes, and augers enter the barn. Trim tree branches that touch or are close to farm buildings.
Destroy all nesting spots, remove rubbish and old machinery from around buildings, store wood off the ground, and keep grass cut around buildings.
Store all feed in rodent-proof containers where possible. Mortalities and edible garbage should also be kept so that they are inaccessible to rodents. Remove any feed spills inside and outside the barn. Reduce water availability in and around buildings.
TRAPPING AND POISONING
There are a number of control methods:
• Snap traps: place traps in dark corners, behind objects next to walls, and wherever rodents are noticed, with the trigger at a right angle to the wall or object. Bait the snap traps with an attractant such as peanut butter or cheese for mice, and bacon, fish, or meat for rats. For rats, leave baited unset traps out for several days before setting them to allow them to get used to them.
• Multiple catch traps: these can catch many mice and are ideal beside doors and feed areas. They can be baited with an attractant such as peanut butter. Place the hole of the device along a wall.
• Glue boards: these catch and hold rodents the same way flypaper catches flies. They’re the method of choice where toxic baits are a concern. They’re not effective in areas where there’s a lot of dust.
• Rodenticides: these include multi-dose anticoagulants, single-feeding anticoagulants, and acute toxins. With multi-dose anticoagulants (such as warfarin, chlorophacinone, and diphacinone), numerous feedings over eight to 20 days result in internal bleeding and death. A break in feeding will allow the rodent to survive. With single-feeding anticoagulants (such as bromadiolone and brodifacoum), one feeding will result in death within days. Acute toxins (such as zinc phosphide) result in death due to physical complications, often from one feeding.
Commercial baits can be purchased in several forms, each having their advantages and disadvantages. Secure bait in bait stations and keep bait fresh, as rodents have an excellent sense of smell and will not eat decayed bait.
Place bait near signs of heavy activity. In the attic, secure bait stations with a nail or wire. It’s recommended to rotate bait chemistry and presentation every few months to prevent bait shyness and resistance.
When handling bait, bait stations, traps, and dead rodents, wear rubber gloves to prevent human scent transfer, accidental poisoning, and disease transfer. All rodenticide products are poisonous to other animals, so ensure they’re not accessible to non-target species. Always observe label precautions regarding use, handling, and storage.
It is more efficient to place more stations with less bait than to have fewer stations with more bait.
The elimination of rats and mice from poultry and livestock barns is extremely difficult. It’s preferable to prevent infestations from occurring in the first place. But once a large population exists, there are options to regain control. If problems persist, contacting a professional pest control company may be the next step.
(Heather McLean is a non-ruminant and biosecurity specialist with Perennia Food and Agriculture Inc.)
