A little knowledge can improve control of house mice, Norway and roof rats.

There's no debate that rodent control can be a major problem in and around swine operations. Disease transmission, feed loss, animal stress and property damage can run up a significant tab.

Effective rodent control requires an investment of time and money. A little knowledge can go a long way toward reducing overall rodent-related costs, explains Ted Bruesch, national technical support manager at Liphatech, Inc.

“It is important to understand the pests' behavior, then use that knowledge to select the most effective tools to control them,” he says.

Rodent Control is a Process

Rodent control is a process, not a program. Because rodents are a never-ending threat, your control efforts must also be ongoing.

Achieving “zero mice” may be impractical, even impossible, for several reasons:

  • Rodents are very prolific creatures. A single female house mouse may produce up to 56 offspring annually.

  • New rodents are constantly drawn to swine production facilities as a source of food and warmth.

  • Rodents are excellent climbers and can squeeze through tiny openings or create their own. Therefore, sealing a building to exclude rodents is a difficult prospect, at best.

  • Rodents are nocturnal and most of their activity goes unseen.

Too often, pork producers implement a rodent control program when an infestation becomes serious, then end it when the crisis has passed.

This approach often results in significant rodent-related losses before the infestation is brought under control. It also requires a larger investment in time and money to knock down large rodent populations.

Know Your Rodenticides

Rodenticides have proven to be the most cost-effective method of rodent control. Two groups of rodenticides are commonly used in swine production facilities: acute toxicants and anticoagulants. A better understanding of each will lead to a cost-effective approach, Bruesch explains.

Acute toxicants — These rodenticides include active ingredients such as zinc phosphide, cholecalciferol and bromethalin. If a lethal dose is ingested, they can kill quickly. However, the high concentrations of these active ingredients tend to make them taste bad. If another feed source is available, rodents may not eat enough bait to be lethal.

Rodents exposed to these materials exhibit distressful symptoms of poisoning, such as paralysis and convulsions. If less than a lethal dose is ingested, the rodent will associate the bait with its discomfort and avoid it in the future. This is commonly referred to as “bait shyness.” It is also important to note that young rodents take clues from their mother about which feed sources are safe to eat.

Anticoagulants — This group of rodenticides comes in two formulations — single-feed and multiple-feed. Anticoagulants inhibit blood clotting, causing rodents to die from internal bleeding. The process produces no signs that the rodent is in distress or pain.

Single-feed anticoagulants contain active ingredients at much lower concentrations than the acute materials, so bait acceptance is improved. These anticoagulants are effective within several days, which is still relatively fast, but not so fast that it triggers bait shyness.

Multiple-feed anticoagulants may take a week or more to be effective.

Use the Right Mix

Both acute and anticoagulant rodenticides have their place in a rodent control process. Using the right mix is the most practical and economical approach.

Acute toxicants are best suited for a quick knockdown of an infestation. The best time to implement this intensive treatment is when the building is empty. Eliminating as many competing feed sources as possible will enhance bait acceptance.

“Don't rely on acute toxicants too long, in order to prevent bait-shy survivors and their offspring from reestablishing the infestation,” Bruesch warns.

When the intensive baiting is complete and the building is restocked, rotate to a palatable anticoagulant rodenticide, such as difethialone or bromadiolone. Rotate the use of these two different-tasting materials to kill survivors that choose not to feed on one bait or the other.

The key to knocking down a rodent population and keeping it down is through the rotation strategy.

Controlling Costs

A little math can help keep rodent control costs down.

A common misperception is that the least expensive pail of rodenticide is the most cost-effective, but there are several factors to consider.

First, consider the “cost per placement.” For example: Product A costs $54.64/pail and Product B costs $64.95/pail. The 18-lb. pail of Product A contains 288 blocks of bait or placements, which equals 19 cents/placement. Product B's 20-lb. pail contains 454 blocks of bait, roughly 14 cents/placement.

In this example, Product B actually represents nearly a 25% cost-per-placement savings.

Additionally, the toxicity of an anticoagulant will impact the effectiveness of a rodenticide and, therefore, the cost/dead rodent.

Remember the Basics

A few fundamental principles will help reduce the cost of rodent control:

  • Understand the rodent. Mice behave differently than rats. Roof rats behave differently than Norway rats. A program cannot be successful unless control methods match rodent behavior.

  • Select the right bait formulation. Block types are best for mice. Avoid using pellets for mice; they hoard them, wasting bait and creating risk. Loose pellets or meal-type baits are excellent for Norway rats because they can be spooned directly into their burrows in the soil. Blocks are great for roof rats because they can easily be secured up high where these rodents live and travel. Make sure the product label allows the application you are considering.

  • Placement is important. Generally, place bait as close to the rodents' nest as possible, but certainly between the nest and feed source. Improperly placed baits waste time and money.

  • Use enough rodenticide. The number one cause of rodent control failures is offering too little material. There must be enough available to allow every rodent to feed on it and ingest a lethal dose.

  • Manage the risks. All rodenticides have risks that must be managed. Properly contain rodenticides with tamper-resistant bait stations in all areas accessible to children and non-target animals.