Go on believing that internal parasites gobbled up in pastures can be managed by simply deworming the cows, or that cattle are parasite-acceptable as long as they look healthy. Jim Ricard of Palestine, TX, knows better.

For years, this commercial cow/calf producer spot-wormed the cows on his ranch. He considered deworming the calves while they were on the cows, but never did until three years ago. Since then, his weaning weights have skyrocketed 130 lbs. and he attributes it to controlling internal parasites in the nursing calves.

“The Texas Beef Partnership in Extension Program (Beef PEP) opened my eyes to how much of a factor worming is. You can see a fat cow or a fat calf, and they can be eaten up with worms but you don't know they're there,” Ricard says.

Ricard began deworming his cows twice a year, but he also began deworming winter and spring-born calves the first part of May when they were worked and vaccinated.

“On a 250-lb. calf, it costs us 34¢/cwt. to worm them, which puts an extra 25-50 lbs. of weaning weight on them. Regardless of the product you use, it's too cheap not to do it. It pays for itself,” Ricard says.

Indeed. Steve Wikse, DVM, an associate professor of large animal medicine at Texas A&M University (TAMU) College of Veterinary Medicine, and the creator of Beef PEP, says 10 field trials in Texas peg weaning weight gains from deworming suckling calves at an average of 0.1-0.2 lbs./day.

Likewise, Dee Whittier, DVM, MS, a University of Virginia professor of large animal clinical sciences, says, “We've done 15 trials in Virginia and have always gotten enough of an increase in weaning weight to make it profitable, some years as much as 50 lbs.” On average, he explains gains in weaning weight due to deworming nursing calves run about 20 lbs. across all the trials. Or about a 1.3-lb. average per day from deworming to weaning.

Further west, Bill Kvasnicka, DVM, a University of Nevada (UN) Extension veterinarian, says they've found similar results. That's despite the common perception, until a decade ago, that internal parasites were few and far between in the West. In fact, in one UN trial, strategic deworming cost $6.60/head and returned an extra 40 lbs. of weaning weight.

While results vary be year and location, Wikse emphasizes, “This is a mighty profitable management practice, and it's time to implement it across more of the industry.”

Better Response All Around

The logic of deworming calves while they're still on their mamas makes sense when you understand how worms steal performance.

In this case, as in most industry discussions, the focus is Ostertagia ostertagi (brown stomach worm), which are prevalent throughout the U.S. According to veterinarians, Ostertagia account for a majority of the damage associated with internal parasites in cattle.

Ostertagia embed themselves in the abomasa of cattle, irritating cells that line the gastric glands and inducing added production of enzymes that suppress appetite. They also interfere with protein metabolism so that less protein is available for antibody production.

Thus, cattle infected with Ostertagia don't consume as much, utilize fewer of the nutrients they do consume, and their immune response is impaired.

Wikse says parasitologists estimate 75% of all losses due to Ostertagia come in the form of production losses, be it reduced fertility or reduced weight gain, etc. They also estimate 70% of the reduced rate of gain occurs because of appetite suppression.

“In the past, we thought if there was enough grass, there was enough to feed the cattle and the parasites, too,” Wikse says. Finally understanding the impact on appetite, he adds, “Now it stands to reason you probably get the most benefit out of deworming when nutrition is the most abundant.”

Moreover, while all cattle are susceptible to the ravages of Ostertagia and other nematodes (parasitic worms), calves are at the highest risk.

“These are the first parasites calves see, and they have absolutely no resistance to them,” Whittier says.

Wherever there's green, growing grass, especially in permanent pastures, odds are that Ostertagia and other nematodes are present. As soon as calves are old enough to start nibbling off the ground, they begin ingesting worms in one form or another.

Cattle build resistance through exposure, but Wikse says it takes two grazing seasons to develop significant immunity. That's why the veterinarians mentioned here also recommend deworming yearlings and first-calf heifers.

Strategic Worming

That's also why these veterinarians aim for strategic internal parasite control, concentrating on both reducing pasture contamination to prevent future infection while ridding cattle of the internal parasites.

“It's the calves from one year that are contaminating the pasture for the next year,” Whittier explains.

While weather and geography again impact prevalence, Whittier says a Virginia Tech study indicates at least 95% of parasite shedding in Virginia cow-calf pastures comes from the calves. “The calves are the major contaminators in the pasture. If you can deworm them as they're getting contaminated, you can keep pasture contamination at a lower level,” he says.

Basically, it goes like this, according to Wikse: Ostertagia can survive as arrested larvae in the abomasa of cattle during the long, hot summers of the South, and during the long, cold winters of the North. Larvae can survive in fecal matter and are released during autumn rains in the South and during spring rains in the North.

On both counts, cattle are exposed to the greatest number of Ostertagia during the rapid growth of cool-season forages, meaning cattle typically receive the most exposure during the spring (March through mid-May).

“Treat cattle when the greatest proportion of the total parasite population is in the cattle and not on the ground,” Wikse advises.

In other words, reducing pasture contamination means deworming calves in the spring.

Whether or not deworming should be routine or based upon an indication of parasite activity is a point of debate.

“I think deworming nursing calves needs to be a standard management practice,” Whittier says. “I think if you wait to see if the fecal egg counts are high, you're too late.”

Collect fecal samples on enough cattle (at least 10-15 head out of 100), and you get an idea how many eggs/gram are present. But that's all you get.

“There is not a good correlation between the number of eggs/gram in a fecal sample and the number of adult worms laying eggs. Plus, the sample measures the prevalence of eggs on the day the sample was taken,” Wikse explains. As the growing season continues, egg counts increase.

Consequently, Kvasnicka believes there is no numeric threshold. If any eggs are present, he says calves should be dewormed. Both Wikse and Whittier agree the safe money is to go ahead and deworm and not worry about the tests.

“One out of 10 or 15 years here, it may be dry enough that you won't get a benefit from deworming; you just account for the cost of that year in all of the others years you do get a benefit,” says Whittier.

That isn't to say fecal egg counts offer no benefit. But rather than rely on them as an indicator of whether or not to worm, Kvasnicka believes a better use is as a barometer of deworming effectiveness and to indicate timing for follow-up treatments.

Kvasnicka says fecal testing costs about $4/sample, but some vendors of deworming products provide testing as a free service.

Of course, there are other indicators producers can use that don't cost more than a little brain sweat. For example, Kvasnicka points out, “Look at the history of the pasture. If it's a permanent pasture, you have to assume it's contaminated.” Conversely, breaking up manure pats by haying pastures or by plowing them up and re-seeding helps reduce contamination.

On the other hand, other pasture management practices can increase the problem. For instance, Kvasnicka explains, “There is a common misconception that pasture rotation and intensive grazing is a way to help manage internal parasites. In reality, it contributes to the problem.”

Product Selection And Timing

If producers want to manage internal parasites strategically, Kvasnicka emphasizes, “You have to use a dewormer that effectively stops egg shedding, one that kills both adults and larvae.”

In the world of anthelmintics (dewormers), Kvasnicka points out that what are termed Class II products act against both adults and larvae. Among those, there are varying degrees of persistent killing power.

“It's important for producers to understand label claims and how to use the products correctly,” Kvasnicka says. “It's extremely important to deal with a veterinarian or parasitologist, know the direct timing of the product and what persistent killing activity in that product means.”

Finally, strategic deworming also demands understanding the parasite challenge by class of cattle. For instance, Whittier explains, “It may well be different in other states, but in Virginia we've never been able to demonstrate an advantage to deworming mature cows.” So, they concentrate on the calves.

In East Texas, on the other hand, Ricard says, “With our wet climate (32-44 in./year) we have a worm-growing paradise. If you worm the cow, too, you know she's doing the best she can for you. If you don't worm her, you don't know.” He's seen an extra kick to weaning weights because of deworming his cows, along with the calves.

Whatever the strategy, Whittier believes you need to deworm the entire group of calves. Doing otherwise is akin to bailing water from a rowboat without fixing the hole in it.

One reason deworming suckling calves is still an industry exception rather than a rule boils down to time and the cost of it.

“Sometimes we want to do everything at a time that's convenient, rather than at a time that's cost-effective,” Kvasnicka says. Depending on where you live, that can mean deworming calves at a time when it's too early to preg-check cows or too late to vaccinate calves, he says.

At the Jim Ricard Ranch, they've figured out how to bundle deworming with other scheduled management practices so they don't have to gather cattle an extra time. Even if that's what it meant, though, the results mean they still would. “We've done it and we've become a believer in it,” Ricard says.

For more information on the Texas Beef PEP, see “PEPing Up Profits,” pg. 42, February 2002, BEEF.

Will Deworming My Calves Pay?

While there are exceptions to every rule, Steve Wikse, DVM, a veterinarian at Texas A&M University says deworming nursing calves, — with the appropriate product at the appropriate time — will likely return net benefit to cow/calf producers if any of these conditions exist:

  • You're dissatisfied with current weaning weights.

  • Calves exhibit clinical signs of parasitism.

  • You run calves on permanent pastures.

  • You run an intensive rotational grazing system.

  • If fecal sampling is done and eggs are present in the fecal sample. (Wikse and other veterinarians recommend deworming all calves without fecal testing.)

Strategic Deworming Considerations

  • When does the grazing season (grass growth) start and end?

  • Will pasture rotation occur or will cattle be moved from pastures to grazing land (from private land to grazing allotments, as an example)?

  • What is the stocking rate?

  • Are the pastures or meadows irrigated?

  • What class of cattle will be grazing the pasture or range?

  • What type of dewormer will be used and when should that deworming product be administered?

  • What is the efficacy of the dewormer against the common nematodes (parasitic worms)?

  • What is the dose, method of administration and duration action of the dewormer chosen?

  • What are the cost of the dewormer and the cost of administering the medication?

Source: Bill Kvasnicka, DVM, University of Nevada