Gil Myers doesn't like to use the term "worms" when he talks about those common internal parasites that affect cattle. He says the word doesn't convey the true economic importance of the parasites.
"I refer to them as 'nematode parasites' of cattle," he says. "This makes it clear that we are talking about parasites similar to what producers are used to dealing with in corn and soybeans. Everyone understands how corn or soybean nematodes adversely affect production of those crops. It's the same with cattle. Nematode parasites can dramatically undermine profits."
Nematodes (also known as roundworms) and flatworms are the two most common families of internal parasites in pastured beef, and they do cost producers a great deal of money. A 2007 Iowa State University study documented a loss of $201 per cow/calf pair annually to the parasites.
Part of the reason that number gets so high is because internal parasites impact the whole herd. A dam with internal parasites, for example, will have reduced milk production. That will decrease average weaning weights on her calves. In addition, when parasite loads are heavy enough, they can reduce body condition; as a consequence, the cow will have a more difficult time cycling and rebreeding.
Seasonal Worm Control
Myers, a veteran livestock parasitologist, operates a commercial cow/calf operation with his wife, Heidi, in LaRue County, Ky. He is also an independent consultant, heading up Myers Parasitology Services. His plan for keeping nematode parasite levels low is based, in large part, on a July deworming program.
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July deworming of cows and calves is listed in the 2015 University of Kentucky Beef IRM (Integrated Resource Management) calendar as a timely management practice for all spring-calving herds. Myers says seasonal worm control in cattle can be compared to controlling thistles—prevent thistles from going to seed, and you prevent future problems. Deworming calves in July prevents shedding of worm eggs. Myers says for every 50 calves not dewormed, 3 million or more eggs can be shed daily onto summer pastures.
"We are deworming the herd to benefit it in two ways," he explains. "One, we reduce pasture contamination. Two, if we deworm spring-born calves in early July, it is strategically timed to allow them to grow without the adverse effects of nematode infections."
Myers' approach to deworming uses free-choice minerals, a tactic he describes as "one of the best-kept secrets in the cattle industry. Essentially, we can manage the nematode population in the whole herd by letting cattle deworm themselves through the free-choice mineral."
This method relies on the use of free-choice minerals with Safe-Guard (fenbendazole). A 50-pound bag of one product will deworm 42,000 pounds of cattle. That pencils out to 28 cows weighing 1,200 pounds each, plus 25 calves that weigh 300 pounds each. Safe-Guard medicated mineral is designed to be consumed in three to six days, after which the producer returns to his chosen mineral program. Myers says there are multiple suppliers of the product, including Southern States, ADM Animal Nutrition, Vigortone and Hubbard Feeds. Treatment costs are $3.50 to $4 per 1,000 pounds of cattle.
While Myers emphasizes the summer program, he says there are many advantages to fall deworming, as well. It helps cattle maximize the benefits of winter hay and supplements, ensuring they come through the winter in better body condition and are ready to cycle and breed on schedule.
"This is also a good way to ensure that cows are not contaminating calving pastures with worm eggs," he says. "That means calves will have lower infection levels early in life and gain faster. One way to look at late-fall deworming is that it's the first step in worm control for the coming pasture season."
In a benchmark study in 2007, North Carolina Extension veterinarian Mark Alley and Extension beef specialist Matt Poore tested the efficacy of various dewormers. They compared an untreated control group at the Upper Piedmont Research Station to calves receiving a generic ivermectin pour-on, a brand name ivermectin pour-on and a fenbendazole drench.
Prior to treatment, the calves, which ranged in age from 6 to 8 months, showed fecal egg counts (FECs) of 300 per gram. Calves treated with the fenbendazole drench showed 100% reduction in FECs. Calves dewormed with pour-on ivermectins showed less than an 80% reduction in FECs, with the brand name (Ivomec Pour-On) performing better (79% reduction) than the generic (73% reduction).
A year later, researchers repeated the study, adding injectable ivermectin. This time, with tests at the Center for Environmental Farming Systems, at Goldsboro, all treatments reduced FECs by more than 90%.
Myers says it's important that, regardless of the class of dewormer used, producers have fecal samples tested to keep track of the performance.
"Anthelmintic [dewormer] failure is an issue in cattle, and producers do need to pay attention to how well they are controlling nematode parasites," he adds. "Rotating product classes, and even using unrelated products together at the same time, are options. Parasite monitoring is key, as it allows producers to objectively evaluate and gain insight into their worm-control programs. Besides, most producers can spare some fresh manure from their herds for testing purposes."
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