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HomeIndustry NewsEffective Parasite Management in Beef Calves: What You Need to Know

Effective Parasite Management in Beef Calves: What You Need to Know

By: M. Wayne Ayers, DVM, Beef Cattle Technical Consultant, Elanco Animal Health

GREENFIELD, Ind. (Jan. 18, 2024) — Cow-calf producers know their deworming program is an essential part of their overall parasite management plan, but what isn’t as clear is which animal to deworm and when. Getting effective results while also reducing the risk of anthelmintic resistance can be a difficult balance to strike. That’s why we must first think about managing internal parasites rather than “a solution in a syringe.” This is especially true for the animals at greatest risk and of greatest potential economic loss.

Young beef calves are at the greatest risk for parasitism because their immune systems have not yet seen parasites. Even when subclinical infections occur and signs are not noticeable, internal parasites can lead to decreased performance of your calves, including reduced growth rates. This in turn, can limit your calves’ ability to reach their full genetic potential and rob your operation of profitability.

Implementing a strategic parasite management program based on geographic location, parasite species present and the age and condition of the animal can be an effective way to decrease the risk of resistant parasites and increase the effectiveness of your deworming protocol.

Understanding internal parasites of concern for calves

While there are around 15 species of parasitic worms that affect cattle, four are responsible for the most economic loss across all regions of the country. There may be regional differences to the following list, so it is important to consult your veterinarian for risk in your area.

  • Ostertagia ostertagi (brown stomach worm) – Generally considered to be the worm of most economic concern, especially in youngstock. They live in the abomasum of cattle causing increased pH, which impacts the digestibility of protein and decreases appetite. The larvae of the brown stomach worm can become inhibited or encyst in the wall of the abomasum during times of harsh environmental conditions. They emerge from this “hibernation” all at one time when conditions improve, called Type 2 Ostertagiasis disease, causing tissue damage that can be permanent. It is important to use an effective treatment before these inhibited larvae emerge.
  • Haemonchus placei (barber’s pole worm) – This parasite attaches to the lining of the abomasum and feeds on blood and serum. The barber’s pole worm can cause severe anemia when present in high numbers. Young animals are most vulnerable to this parasite. The female barber’s pole worm can lay up to 10,000 eggs per day when conditions are favorable. So, pasture contamination can become a problem.
  • Cooperia sp. (cattle bankrupt worm) – There are several species of this parasite that affect ruminants with C. punctata and C. oncophora being the most common in cattle. These parasites live in the small intestine and absorb nutrients from the host. While not highly pathogenic by themselves, they appear to be synergistic with O. ostertagi by further depressing feed intakes and therefore gains.1
  • Trichostrongylus axei (small stomach worm) – This parasite lives in the abomasum, attaching to the stomach wall and feeding on protein and blood. This parasite can cause diarrhea, dehydration and emaciation.

Identifying parasite species present

The first step in developing an effective parasite management program is understanding which parasites are present in your cattle. Several tools exist to evaluate the presence of parasites, the species present and effectiveness of a given treatment. Work with your herd veterinarian to conduct this evaluation.

Species-specific quantitative analysis (SSQA) allows us to understand if a group of or individual animals have parasites, what species are present and in what proportion. This often allows for a more strategic and targeted treatment protocol. Knowing which herd groups have parasites, what species are represented and in what proportions with SSQA is a critical step for choosing your dewormer and as part of your overall parasite management program.

Choosing a dewormer

Dewormers come in several different forms, pour-ons, injectables and oral drenches, and there are currently three dewormer classes available in the U.S. for cattle: benzimidazoles, imidazothiazoles and macrocyclic lactones.










While the dewormers listed above have similar indications, there may be differences in parasite stage effect or efficacy. For example, Cooperia sp. tends to be less sensitive to the avermectin sub-class. Therefore, if this parasite is of most concern for your operation, you may want to choose a dewormer from a different sub-class, such as milbemycin or a different class. When resistance to a given parasite has been demonstrated it can be necessary to use two different dewormers at the same time from two different classes.

Timing of treatment based on the predominant parasite stage may also influence a choice of a dewormer. If you are deworming cattle when it is very likely the brown stomach worm larvae have encysted, then you may not want to use a benzimidazole because some benzimidazoles are less effective against larvae than a macrocyclic lactone.

Timing matters

As imperative as it is to use the right product in the right animal, it is equally important to use the product at the right time for the best results. Working with your herd veterinarian can help identify the strategic times to deworm to make the most out of your management practices.

While broad-spectrum pour-on dewormers (endectocides) should only be used when internal parasites are the primary target, they can provide added benefits for lice and fly control. During the fall, producers can capitalize on the secondary benefits of deworming with endectocides to help keep lice at bay until winter treatment and to knockdown late season flies.

Proper dosage and application are important

To ensure effective deworming, always follow the product label and dosing instructions and accurately weigh each animal to prevent underdosing or overdosing. Underdosing can lead to resistance and overdosing can be a waste of money and may lead to adverse reactions. Proper dosage ensures the dewormer is being utilized to its fullest potential and you are making the most of your investment while reducing the chances of anthelmintic resistance. When applying a pour-on, use an applicator gun to ensure the product is evenly applied along the midline from the withers to the tailhead.

Internal parasites in young calves can lead to significant economic losses for your operation. By implementing a strategic parasite management program and going beyond traditional approaches you can help to mitigate the negative impacts of parasites and enhance your calves’ well-being, all while protecting your investment. To learn more, talk to your Elanco technical consultant or visit or

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