Science and Weather Impact Deworming Decisions

By : Terri Queck-Matzie

Internal parasite control in cattle requires timing, planning and persistence. Deworming must be done often enough to control pests and reduce the economic impact of infestation, yet not too often, lest cattle develop anthelmintic (dewormer) resistance.

There is no magic formula. Every ranch, every herd, and every season is different.

Jody Wade, Professional Services Veterinarian for Boehringer Ingelheim, says, “The biggest thing we’re seeing right now is issues that are popping up maybe where the dewormers folks are using are not working like they should, and we think that could be some resistance issues. So the big push from most of the parasitologists from across the country is being more science-based in our deworming decisions – on how we’re going to deworm them, time of year that we’re going to deworm them, and the products that we use – based on science.”

Wade advocates the use of fecal egg counts (FEC) to confirm parasite problems before implementing a plan. Wade says checking just 10% of the herd will give a good snapshot of the problem.

Performing a fecal egg reduction test (FECRT) is helpful for producers and vets wanting to determine the efficacy of a specific product bytesting before and after treatment.

“Some of the dewormers are better at certain parasites than others are, so being more specific toward the parasite with your choice of dewormer is a smart move,” says Wade, “and can help reduce resistance by not over-using product. Producers get used to the things they’re using and they assume that it’s working. Unless we’re actually using a little bit of science to check, you never know.”

Across the industry, producers and veterinarians are taking measures to reduce the effects of anthelmintic (dewormer) resistance. Some advocate refugia, leaving enough non-resistant parasites behind to breed with the resistant ones, thus slowing the rate of genetic resistance. And use of two types of dewormer concurrently is recommended, increasing the possibility of killing more resistant parasites.

Timing matters

Wade says internal parasites may be a greater issue this year than some years due to wet winter and spring conditions across much of the South, creating a perfect breeding environment for the pests. Jason Banta, Associate Professor and Extension Beef Cattle Specialist at Texas A&M AgriLife Research & Extension Center at Overton, Texas, says he’s not sure the weather conditions will make the problem worse, but it will affect timing. “The norm is a strategic treatment time of 28 days, generally late May into June and again in November-December,” says Banta. “With the long, wet spring, that timetable will likely be delayed. You want the dewormer to kill the parasites in the cow, but you don’t want to her to shed the eggs into a favorable environment. It needs to be hot and dry so the eggs don’t live as long.”

He says for the cow/calf operator, deworming treatment may be delayed 3-4 weeks, while the stocker is likely to treat all calves on arrival unless their history is known regardless of exact timing.

Banta advises checking the slaughter withdrawal date of your product if adjusting your timetable, and its flammability. Make sure branding is done before use of a flammable pour-on product.

And, of course, be sure to follow good management practices that reduce exposure to internal parasites, and remember internal parasite control is only one part of an overall animal health plan developed with a  veterinarian.

Studies have shown cattle entering the feedlot phase of production with high fecal egg counts are more likely to exhibit a low rate of gain and low back fat and marbling scores, despite being treated upon arrival, suggesting internal parasites can have long term implications for cattle performance

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