Rodent control on the farm is an essential aspect of both biosecurity and property damage.

Ron Forquer, eastern business manager for Motomco, addressed the topic recently at the Penn State Dairy Nutrition Conference. Rodents carry 45 diseases, 35 of which can be directly or indirectly transmitted to livestock and humans.

“Diseases live within their bodies, on their hair and excreted in urine and feces,” said Forquer. “Rodents are accustomed to living with humans and farm animals, which increases the likelihood of disease transmission.”

Rodents spread disease when livestock eat feed contaminated with rodent urine and droppings, and through direct contact with livestock by parasites such as fleas and mites. Rodents can increase cull rate, decrease production, decrease slaughter value, decrease feed efficiency and lead to premature culling of clinical or infected animals. There’s also potential loss of investment in youngstock that have been exposed to pathogens since birth.

Feed contamination is a significant issue. Rodents contaminate 10 times the amount of feed they eat. “One rat consumes about 25 to 30 pounds of feed per year,” said Forquer. “One mouse consumes about two to three pounds of feed per year. It’s estimated that rodents damage up to about 20% of the world’s food supply.”

The presence of just one rat costs about $2 in feed. That doesn’t seem like much, but 100 rats cost $200, and 2,000 rats will cost about $4,000 in feed loss in one year.

In the U.S., the economic cost of rat and mouse damage is estimated at about $19 billion – more than any other animal species. Damage comes in the form of chewing and gnawing on curtains and insulation, which results in increased energy and repair costs. Chewing on wires creates fire hazards, and it’s estimated that about 20% of unknown fires are caused by rodents chewing on wires.

House mice are sexually mature at about four weeks of age, and they can have up to eight litters each year with about five or six young in a litter. A population of 50 to 60 mice in a typical ag facility can increase to 2,000 mice in just six months.

Rats typically live in burrows, while mice tend to live in quiet, undisturbed areas, especially corners. Rodents live in colonies headed by a dominant (alpha) male and an alpha female that have the best access to food and shelter. If the alphas are killed, the weaker members shift to more desirable habitats and food sources. Rodents are nocturnal by nature. Daytime activity of rodents is a sign of a large infestation.

The first step in rodent management is species identification and habitat inspection. The Norway rat and the house mouse are present throughout the Northeast, while the roof rat is more common in the Southeast.

Droppings are a key sign of rodent presence and are commonly found in grain storage or spillage areas. When inspecting areas for rodent activity, look for droppings, odor, rub marks, evidence of gnawing and burrows. If burrows are evident, kick them in and return later to see which ones opened up – those are active burrows. Bits of insulation or cloth outside a building are signs of nesting.

Rats typically tunnel under a foundation – gaps under and around doors are a major rodent control challenge. Walls and frequently used paths will have rub marks from rodents’ oily fur. Metal plates should be used to repair rodent entry areas.

Sanitation helps prevent rodents from setting up home. Remove potential food and water sources and clean up spilled feed, garbage and debris in and around buildings. Forquer recommended creating a three-foot crushed rock or cement zone outside of buildings. Eliminate all grass and overhanging trees that provide cover from predators.

Baiting is the most effective means to manage rodents. “There are two measures of a good bait: palatability and efficacy,” said Forquer. “They have to eat it, and it has to kill them.”

The active ingredient in rodent bait is either an anticoagulant or a neurotoxin. About 65% of baits are anticoagulants, which can cause secondary poisoning if another animal consumes the rat or mouse that has eaten bait. Neurotoxin baits have far less risk of secondary poisoning. Good quality rodenticides are made with human food-grade materials and contain components that meet rodents’ dietary needs, which helps entice them.

Rodents have high sensitivity to taste and use tasting and nibbling to check quality. If bait is stale or moldy or they detect odor, rodents won’t eat enough bait to kill them.

Forquer described mice and rats as neophobic – disliking anything new. When baiting for rats, allow about a week for them to start taking bait. Once they are accustomed to bait, they’ll consume a lot.

“Rats eat about one ounce in 24 hours,” said Forquer. “They’ll hoard enough food to last three weeks. Mice eat about three grams in 24 hours in small feedings.”

Because numerous rodenticides and bait types are available, Forquer suggested selecting single-feed products. “They get sick in a single feeding and don’t have to come back to eat more,” he said.

Check stations as often as necessary if bait is disappearing. Always check bait stations at least once a month. Weekly follow up treatments should eventually eliminate all social levels.

Bait should be rotated between anticoagulants and neurotoxins. “Neurotoxins help disrupt bait shyness and prevent resistance in rodents to rodenticide,” said Forquer. “Rodents have a good sense of taste and like different flavors.” He recommended using a neurotoxin bait in colder weather because that’s when rodents move inside from fields.

The EPA requires that outdoor, above-ground baiting with rodenticides of one pound or less be placed a bait station. “Tamper-resistant bait stations are required if within reach of a domestic animal, non-target wildlife or children under six years,” said Forquer. “Other types of bait stations may be used in settings such as around livestock production, buildings where exposure to children and non-target wildlife is likely.” Stations also protect bait from dust and moisture to keep it fresh.

When baiting outdoors, space the stations around building exteriors every 50 to 100 feet. “You can put them closer in high-pressure areas between buildings,” said Forquer. “Intercept rodents before they get into a building.” Indoor bait boxes should go in corners because those are the busiest spots.

Wear gloves when placing bait – gloves protect hands from becoming contaminated with toxic substances and help prevent bait aversion when scents are transferred to bait by human hands. Secure bait on rods to force rodents to consume it in the station and prevent hoarding.

Additional strategies include baiting burrows with pellets or meal bait. “Use pellets in burrows because they can knock it out anything bigger,” said Forquer. “Tracking powders are restricted use and require licensing.”

It’s important to keep bait stations clean and supplied with fresh bait to increase consumption. Fresh bait is ideal, with smaller placements more often. Rodents have options – make sure you’ve provided the best one.

by Sally Colby