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Benzimidazoles, or white dewormers, are an important tool for managing internal parasites, but it’s essential to use this dewormer class correctly.
Leonor Sicalo Gianechini, DVM, PhD, University of Georgia, along with Nathan Meyer, DVM, PhD, Boehringer Ingelheim, offer these tips to ensure your oral drench delivers the desired results.
Correct placement
An effective purge with white dewormers needs careful placement of the dewormer itself.1 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 you don’t place a drench far enough behind the tongue, the esophageal groove reflex may send the drug into the abomasum instead of the rumen, which reduces 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 gets 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 make sure that 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, which affect many aspects of cell function.1
Benzimidazole dewormers are usually in and out of an animal’s system in a couple of days.1
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.”
Oral drenches work well because the gastrointestinal tract is the largest absorptive surface of the body, says Dr. Meyer. That large surface area means the oral drench has more contact with parasites, which improves its efficacy.
Correct dose
For high product efficacy, dosing needs to 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 make sure that we’re giving 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 it’s a uniform product we’re giving 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.
Make sure the applicator’s dose is set appropriately, because the dial can easily get bumped. Allow minimal air into the plunger, especially with a new bottle. You can ensure air is out of the system by checking the barrel.
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 fit into a well-rounded and sustainable deworming program.
