Traditionally, cattle deworming tends to be done when and how it’s convenient. At fall preg check, we pour everybody with either the cheapest product we can find or maybe that name-brand product. We don’t worry about resistance and significant production losses. Calves might get dewormed at weaning; bulls get a quick dose of something at semen check. We’ve gotten by relatively unscathed, and everybody looks a little bit better over the next few weeks out on corn stalks/winter grazing or wherever they go.

Veterinarians would like to challenge you to rethink this approach. Each year, we hear more and more about the emergence of resistant gastrointestinal parasites. In the past, this has been an issue of the southern states, yet as more and more studies have shown, resistance can be seen all over the US and the world! Cooperia and Haemonchus spp are already showing resistance to our macrocyclic lactones (Ivermectin products) in the south and north, with evidence of emerging resistance to Ostertagia in the south. Up to 90% of tested operations have shown resistance. Some parasites can cause significant health issues, while others cause more subclinical production losses and decreased immune response.

The goals of an ideal gastrointestinal parasite control program are eliminating clinical disease, minimizing subclinical/production losses, and slowing down resistance while promoting sustainable beef production.

Let’s start with the cow herd. These ladies tend to be less susceptible to losses due to parasites based on age, general health, and grazing habits. There are multiple approaches to best deal with these gals, which should be a discussion with your veterinarian. However, a couple of main ideas have been strongly recommended:
1) use a combination therapy approach (ex. Fenbendazole and Ivermectin-based products) as this will have an additive effect and a broader spectrum of efficacy.
2) refugia – leaving some susceptible parasites within the system (not treating the heaviest, healthiest 10-20% of middle-aged cows). These ladies are most susceptible to losses via decreased milk production. Therefore deworming prior to calving (preg check time is typically most convenient) is in their, and our, best interest.

The nursing calf: because they don’t graze early in the calf’’s life, they are unlikely to have a substantial gastrointestinal parasite issue. As they grow and start to graze, by the end of the summer, you can count on those spring calves to have a significant parasite burden. Also, calves excrete the highest number of parasite eggs per gram of feces in the whole cow-calf production system. Don’t skip deworming these kids! Every calf should be dewormed with a combination of products, ideally at pre-weaning. When combining these products, it is recommended to avoid pour-ons for the calves, as the absorption of these products can be inconsistent, and the efficacy against Cooperia sp. is considered poor.

As calves advance through the production system, it is recommended that stockers be dewormed when putting out to fall grazing, again with a combination of products and following the refugia concept. Deworm all feedlot cattle with either a combination or a “white wormer.”

Feeders in a drylot setting are unlikely to become reinfested with gastrointestinal parasites, yet we cannot forget about the re-emergence stage of Ostertagia. Therefore using at least a “white wormer” is very important.

Bulls tend to be forgotten, yet generally should be managed similarly to stockers – refugia, combo products, and before breeding. These boys can be the most important carriers/shedders of GI parasites. It is generally easiest to deworm them at BSE time, and this can be repeated when taking them off cows and moving to winter locations.

Above all else, be sure you are discussing protocols and concerns with your veterinarian. What works for another operation may not be ideal for yours, and your vet is trained to help you select the best timing and products for your system. Your vet may recommend Fecal Egg Count Reduction Testing (FECRT), as this is a great way to measure the efficacy of your product(s). It is easy, albeit a bit messy. There are multiple products and protocols, and navigating this can be difficult, which makes talking to your veterinarian even more imperative.