Control Parasites this Spring
to Head off Pasture Buildup

Fewer parasites mean fewer production losses for producers.

Spring parasite control — while ultimately helping to protect herd health and performance — is more about reducing levels of pasture contamination than curing sick animals.1

"Only 5% to 10% of parasites in the total system are actually in cattle at any given time,"1 explains Frank Hurtig, director, Merial Veterinary Services. "A single cow can pass millions of parasite eggs during the grazing season, which is how the remaining 90% to 95% of parasites end up on pastures — set to infect grazing cattle."

Targeting parasites in the spring hits parasites at a key stage in their life cycle and helps keep cattle from becoming parasite factories,2 he explains. This reduces the number of parasites on pastures and helps producers proactively avoid losses or reduced productivity.

"Many cattle producers only control parasites at the end of the grazing season. But at that point we've already lost growth and productivity, and contaminated the pasture with even more parasites," says Bert Stromberg, parasitologist and professor at the University of Minnesota. "If producers are only going to treat once, it should be at spring turnout."

Northern producers may skip a spring treatment because they mistakenly believe a cold winter has taken care of parasites for them, or that one fall treatment is enough to protect cattle all year, Hurtig says.

"Parasites can and do survive the winter on pastures,"1,2 Stromberg says. "If producers are under the impression that they solved their parasite problem with one treatment in the fall, they will miss the parasites that are present on pasture as cattle enter the grazing season."

Research in Oregon found that parasites were transmitted even during freezing temperatures.3 And those not picked up during the winter can survive to spring. A blanket of snow helps survival,4 Stromberg notes. It insulates parasites and is like putting them in the refrigerator, which is exactly where he keeps his live specimens for research.

"Parasites such as Ostertagia, also known as the brown stomach worm, effectively survive the winter in an inhibited juvenile state in the lining of a cow's stomach,5 but they also can burrow into the soil where they are protected from severe temperatures,"2 Hurtig explains. "When warm weather arrives, infective juveniles migrate onto the grass where they are picked up during grazing."

Parasites overwintering in cattle also become active in the spring, developing into egg-laying adults and completing their life cycle.5 This flurry of parasite activity means parasite infection peaks during spring and summer.

"Fortunately, the longer parasites spend on pastures once temperatures increase, the less likely they are to survive,"2 Hurtig says. "That gives us the opportunity to successfully interrupt their life cycle with spring parasite control."

A spring treatment with an Ivomec® (ivermectin) Brand Product helps clear cattle of parasites around the time overwintering parasites hit their peak. And, Hurtig says, those products keep working for 14 to 28 days — depending on the parasite and the product used6 — to help protect cattle from parasites they pick up during late-spring grazing.

"Not all parasite control products offer this important extended window of protection," Hurtig notes. "Drench-type or white dewormers are only effective the day of treatment,6 and not against inhibited Ostertagia at the normal dose, which means that, at most, they only control the 5% to 10% of the parasite population that is actually in the cow at that point, not the 90% to 95% of parasites that are found on pastures."

"Parasite control is strictly a numbers game," Stromberg says. "We'll never eradicate them, but we can reduce their numbers. The more parasites we have, the more damage we have." That's why he says reducing pasture contamination is so important.

"With spring treatments we remove the parasites from the host so they never have the chance to contaminate the pasture," Stromberg says. "If we can do that, we can go longer with fewer parasites in cattle and fewer losses."

Hurtig encourages cattle producers to make sure they use a product they trust for this key spring treatment. He notes that Ivomec Brand Products are backed by a 100% Product Satisfaction Guarantee.

"Spring parasite control should be part of every cattle producer's management strategy. It helps cut pasture contamination and prevent losses," Hurtig says, encouraging producers to consult with their veterinarian on how to incorporate spring parasite control into their management plan.

Editor's Note: This article is adapted from a news release provided by Merial.
1Stromberg B. Strategic deworming: A Northern cow/calf perspective. Merial Symposium 2005.
2Hildreth M. Economics and control of cattle-worms in beef cattle: a Northern perspective. Academy of Veterinary Consultants Meeting. December 2008.
3Rickard LG, Zimmerman GL. The epizootiology of gastrointestinal nematodes of cattle in selected areas of Oregon. Vet Parasitology 1992;43:271-291.
4Stromberg BE. Environmental factors influencing transmission. Veterinary Parasitology 1997;72:247-264.
5Myers GH, Taylor FR. Ostertagiasis in cattle. J Vet Diagn Invest 1989:195-200.
6Based on data provided in FDA Freedom of Information summaries.

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