Benzimidazoles, or white dewormers, are important tools for managing internal parasites, but it’s essential to use this class of dewormers correctly.

Leonor Sicalo Gianechini, DVM, PhD, University of Georgia, and Nathan Meyer, DVM, PhD, Boehringer Ingelheim, offer these tips to ensure your oral drench delivers the desired results.

Correct placement
An efective purge with white dewormers needs careful placement of the dewormer itself. Restrain the animal in the chute, or at the very least a head catch, says Dr. Meyer. Insert the hooked end of the applicator at the commissure of the lips (where the lips come together). Angle the hook toward the back of the mouth in the cheek so it gets behind the tongue, not on the tongue.

Dr. Sicalo Gianechini adds that if a drench is not placed far enough behind the tongue, the esophageal groove reflex may send the drug into the abomasum instead of the rumen, reducing its efficacy. “You want it to go to the rumen because with benzimidazoles, that rumen acts as a reservoir,” Dr. Sicalo Gianechini explained. “The drug is going to mix with the particles, and then it is going to be slowly released into the abomasum. The abomasum has an acidic pH, causing the drug to be dissolved and absorbed. That is critical for benzimidazoles, so the proper technique of getting it behind the tongue is absolutely a must.”

Drenching is a task in which slow and steady get the best results.

“Sometimes, based on how cattle are moving around, patience is our biggest ally,” Dr. Meyer said. “You have to take your time and ensure the hook is inserted fully without forcing it. We can damage the mouth or esophagus if we force it. It may take some maneuvering to get the V of the hook clear to the commissures of the lips. Then depress the applicator all the way, slowly and steadily.”

Impatience, and thus improper placement, can also result in regurgitation and wasted product.

Placement affects efficacy
In addition to avoiding regurgitation, correct drench placement affects the product’s efficacy. Benzimidazole drenches purge internal parasites by interfering with the parasites’ microtubules, affecting many cell function aspects.

Benzimidazole dewormers usually enter and leave an animal’s system in a few days.

Dr. Sicalo Gianechini emphasized, “If you want good drug efficacy, the main thing is that the worm has to be in contact with the drug for a certain period of time, so that the drug can pass through the cuticle (in nematodes) or tegument (in cestodes) and enter the parasites. So, the longer the contact between the active ingredient and the parasite, the better.”

Dr. Meyer says oral drenches work well because the gastrointestinal tract is the largest absorptive surface of the body. That large surface area means the oral drench has more contact with

Correct dose
For high product efficacy, dosing must be accurate — and accurate body weight leads to accurate dosing. Dr. Meyer recommends using a low-dose, highly concentrated product to do the job cost-effectively. Ideally, you’d be able to weigh cattle by using a scale on the chute. If that isn’t available, you could use a recent body weight or calculate the average from a sale barn weight ticket or the truck and trailer weight.

If dosing a group without accurate weights, Dr. Sicalo Gianechini suggests getting a weight on the heaviest in the group, and dosing according to that animal.

“Underdosing is a high-risk practice when it comes to the development of drug resistance,” she noted.

Dr. Meyer explains that underdosing parasites causes them to create a response to the drug instead of being killed. Because a parasite’s life cycle is short, that response gets carried into the genetic material of the next generation. This passed-down response can lead to resistance.

Be sure to follow the label directions for administration.

“Benzimidazole products can settle in the bottle, and we want to make sure we’re mixing the bottle and giving a uniform dose,” stressed Dr. Meyer. “We also want to ensure we give the active ingredient at the correct concentration. I always try to shake the bottles every 20 to 30 head when I’m processing cattle to make sure that a uniform product is given to the animals.”

It’s important to maintain a temperature of 77 degrees or cooler, and above freezing, so efficacy is highest when the product is stored indoors. When working during a hot day, Dr. Meyer suggests using a smaller bottle size or storing it in a cooler.

Ensure the applicator’s dose is set appropriately, as the dial can easily get bumped. Allow minimal air into the plunger, especially with a new bottle. You can check the barrel to ensure air is out of the system.

If possible, disinfect the applicator between cattle with a chlorhexidine solution dip, Dr. Meyer suggests.

Before choosing your oral drench, consult with your veterinarian. Proper diagnostic testing will verify whether a drench or a different product is best for your operation’s parasite load. Your veterinarian can help decide how drenches fi t into a well-rounded and sustainable deworming program.