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Well-timed deworming best value

Deworming your cow herd might be compared to carpet bombing vs. laser-guided bombing.

Well-timed deworming best value

Deworming your cow herd might be compared to carpet bombing vs. laser-guided bombing.

Deworming at the wrong time is a lot like carpet bombing: It costs a lot of money, and while it may wreak havoc with the target population, ultimately it may not win the battle.

Deworming at the right time is more like sending a laser-guided bomb straight into the enemy’s bunker, taking out nearly the entire population of troublemakers with one well-placed, well-timed attack.

The first problem, according to parasitologists, is gathering the intelligence for this precision attack. Depending on where you live and what species of worm ails your cattle, deworming might be best done early in the spring, late in the spring, in early summer, or maybe in the fall. Sometimes, of course, the deworming war requires more than one well-timed and well-placed strike.

It’s really a matter of figuring out when the weak point in the parasites’ life cycle occurs and then balancing the attack to take advantage of that, says Mike Hildreth, a zoologist and microbiologist at South Dakota State University.

Hildreth’s research has shown deworming shortly after spring turnout in the Northern Plains may offer the most bang for the buck.

Many northern beef producers have long thought internal parasites suffer significant winterkill and therefore don’t create many problems until later in the year.

Not so, says Hildreth. His research has shown most worms, including the ever-problematic brown stomach worm, can overwinter fairly well in the soil and by greenup are ready to reinfect cattle at high enough levels to cause economic loss through the summer.

“In the old days they would fall deworm, especially with drenches, and that would do a pretty good job cleaning them up for the fall and winter, but then they would get reinfected when they went out on spring pasture,” Hildreth says.

It’s not always easy to hit the prime time, Hildreth admits, because that’s probably a couple of weeks after greenup (or turnout). Such timing would kill most worms before they reproduce and do much damage. It also would carry out residual control for possibly four more weeks, which would prevent significant reinfection for the rest of the very short northern green-grass season and the limited number of generations the worms can produce in northern summers.

“In our area it makes sense to deworm in the spring and then use a pour-on for lice control in the fall,” Hildreth adds.

On the other hand, Texas A&M University parasitologist Tom Craig says research he and others have conducted in the Gulf Coast region of Texas shows most years a summer deworming likely pays the highest dividends. Typically, this is between mid-May and mid-August, he says.

Heat and dryness are the biggest enemies of most internal parasites in that environment. Parasites that affect cow-calf operations, particularly the brown stomach worm, are typically in an “arrested state” during the summer, Craig says. This means they are in the early stages of development, not yet reproducing and not yet causing harm to the gastric tissues.

Therefore, treatment in the summer, while the larvae are in arrest, will prevent reproduction and the ensuing damage from occurring as large numbers of parasites emerge and feed, Craig says.

An ideal deworming should accomplish two things, he notes:

1. Protect the treated animal from disease.

2. Protect the pastures from large numbers of larvae a month or two later.

In the far southern regions, this is what the summer treatment does best. Craig’s research, in particular, shows the brown stomach worm begins to enter this inactive state in cattle’s bodies about mid-May.

Incidentally, Craig says, there appears to be a point in far South Texas, about where the southernmost King Ranches are located, where the brown stomach worm ceases to exist in significant numbers.

Also, those who need to battle liver flukes in the wet southeastern regions would need to attack those enemies in the fall, Craig adds.

“Sometimes the drug companies want to use a single approach with deworming strategies, but one approach just doesn’t fit all,” Craig says.

In the end, though, these people and others know the best time to deworm sometimes isn’t the most practical or most effective time.

As Jim Neel, University of Tennessee beef specialist quips, “I always said, when you get ’em up or can catch ’em is a good time to deworm.”

Practices aid worm control

• Grazing rotation: When a pasture is at rest (not grazed), immature worms find no hosts and eventually die. This depends on weather, but it might take two months in the summer or as long as six months for a high level of mortality.

• Pasture drag: Using a harrow to break up manure piles has some value because the parasites are exposed to drying and perhaps to heat. It’s more effective during hot, dry summer months. However, for a couple of weeks after pasture dragging, immature worms can be more numerous.

Parasites thriving this year

Last year’s drought in the Southern Plains and wet summer in the Northern Plains have put much of U.S. cattle country at risk for a heavy parasite load.

Tom Craig of Texas A&M University says this is the first time he has seen clinical ostertagia, or brown stomach worms, so bad that cattle actually have gotten sick. Therefore, it’s likely pastures and cattle are carrying a heavy load of parasites.

Mike Hildreth, South Dakota State University, says the wet, cool summer boosted populations in the northern regions, and the following heavy snow load has protected them from the extreme cold of this winter.

As a result, spring deworming may be the best process in southern as well as northern areas this year. Craig says this doesn’t change the recommendations a lot, but he says with a good residual dewormer, April to June should be a great time frame for southern dewormings.


THE ENEMY: Cross-section of one brown stomach worm larva looped inside a gastric gland.

Photo by Louis Gasbarre

This article published in the April, 2010 edition of BEEF PRODUCER.

All rights reserved. Copyright Farm Progress Cos. 2010.

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