Summer is here, and that means cattle are grazing, and with it, dealing with parasites. Deworming is a herd management practice that can yield a significant return on investment. However, for producers to get the most effective results from their deworming program, while reducing their impact on anthelmintic resistance, mass treatment may not be the best approach to parasite management.
Impact of parasites
“Parasites are hard on cattle,” says Lee Jones, DVM at Boehringer Ingelheim. “There are a variety of parasites that can affect an animal’s stomach, small intestine and large intestine. Parasites are so destructive because the guts are absolutely critical in digestion and nutrient absorption, and anything that affects the function of the GI [gastrointestinal] tract is going to put that animal at risk of being malnourished.”
Unfortunately, because you can’t see what’s going on inside the animal, parasites are often missed until they cause so much damage the animal shows clinical signs of distress.
“Internal parasites are difficult because there are very few external signs until you get to a place where the animal has already become very obviously damaged,” says M. Wayne Ayers, DVM, beef cattle technical consultant at Elanco. “Most of our losses are in things that we can’t measure, like modification of the immune system.”
Parasites affect cattle on grass the most, meaning cow-calf and stocker operations. They can reduce weight gain and milk production in cows, which reduces calf weaning weights, weight gains and female fertility rates, as they're not going to breed back as quickly or at all, Jones says.
“Parasites can also cause you to not get the most out of your grazing because the parasites reduce your efficiency or tonnage you can take off a pasture,” says Eric Moore, DVM with Norbrook. “Proper utilization of your resource is key in our system of sustainability. You have limited resources that you must use to [their] maximum.”
The long-term effects of parasites are relatively unknown. “There's a lot of things we don't know about yet when it comes to the long-term effects of parasites,” Moore says. “From fetal programming, we know when a fetus is exposed to malnutrition – from parasites, drought, etc. – it can have long-term effects on that animal.”
He adds, “The fetus may also build an immune response to the parasite, as it would if the mother was infected with a disease, and build a response for the next time it is infected later in life.”
Treatment
Unfortunately, you will not get rid of parasites completely. Parasites are resilient and adapt quickly.
“Cattle are constantly exposed to parasites,” Moore says. “You're basically playing a numbers game, trying to keep levels down as low as you can to reduce exposure and prevent continued contamination from reinfestation.”
Producers have three options for dewormers: oral, injectables and pour-ons, says Jones. Oral dewormers are gone in 48 hours as they quickly work their way through the animal and “purge” the parasites. Injectables and pour-ons give three to four weeks of coverage, as they take longer to get through the animal’s system. Extended-control dewormers give up to 150 days of coverage, allowing for longer protection for extended times of grazing, Jones continues. But your decision on the dewormer you use all depends on the type of parasites you are dealing with and which products provide the best coverage for your operation.
It's important for producers to understand the different classes of dewormers because they work differently. Injectables and pour-ons are in the same class. Though there are multiple different name brands plus generics, they are all the same class of dewormers. Oral products are in a separate class. When the effectiveness of one product declines, all brands in that same class are affected. That’s why we recommend rotating classes, not just brands or methods of administration.
Injectables tend to be more consistent and accurate, compared to pour-ons, because the proper dose can enter the animal’s system easily rather than having to be absorbed across different hair coats, Moore says.
“Some animals are just more susceptible to parasites than others,” Jones says. “Taking fecal samples and testing will allow you to treat and prevent parasites the right way. It’s important that we begin to monitor if your parasite program is working. Ask that question. Don't take it for granted that you used a product and that it worked.”
It’s typically unnecessary to treat your whole herd, Ayers says. Animals 4 years old and older typically have developed some immunity to parasites, and their immune systems will kill those larva as they eat them. This means these animals tend to have low parasite egg counts and don’t require frequent deworming. You’ll receive a greater return on your investment by focusing the most effective treatment on younger animals like yearlings and calves, leaving older animals untreated, if possible, as a source of refugia, Ayers adds.
“It’s all about trying to make sure that we're using the right product, on the right animal, at the right time,” Ayers says. “Timing is very important. There is no benefit in deworming too early because cattle can become reinfected, and you’ll have to deworm again, wasting money and risking resistance.”
Overdosing has the risk of changing withdrawal times, in addition to an added cost.
While there is a well-known economic fallback to overdosing, it is even more dangerous to underdose because it enhances the risk of creating resistance because the product concentration may not be high enough to actually kill the parasites, Ayers says. It kills the most sensitive parasites but leaves the ones that are a bit hardier and have some tolerance to the product used, thereby allowing them to survive and reproduce.
Proper grazing can also help prevent parasite infestation, Moore says. Larvae live on the bottom third of the plant. Preventing animals from overgrazing and getting that far down on the plants will limit their exposure to the parasites.
You’ve probably heard it before, and you’re going to hear it again: Work with your veterinarian to develop a plan for dealing with parasites. Parasites affect every operation differently. It all depends on your climate, temperatures, precipitation, the time of year and pasture conditions.
Resistance
It’s been 25 years since the last parasite treatment drug was developed, Ayers says. And while it’s still highly effective, it is increasingly important to reduce the risk of resistance in your herds, as there are no new molecules on the market to treat resistant parasites.
Rotating classes of dewormers and using them properly creates a better chance of preventing resistance, Jones adds.
“We need to be cognizant and more proactive about being good stewards of the products that we have so that they last longer,” Ayers says. “Using the right product, on the right animal, at the right time is better for your herd’s health and productivity.”
