Rational thinking would cause one to figure, in a drought as epic as this year’s, that worm larvae have a snowball’s chance of surviving. Pastures have a crisp, toast-like patina and there isn’t enough moisture and green grass to entice any self-respecting Ostertagia larvae to leave that nice, homelike cow patty and brave the elements.

One would be wrong. A drought does not play fair. Neither do parasites.

“What’s interesting about drought is it seems to increase the risk of internal parasites,” says Gerald Stokka, Extension livestock stewardship specialist at North Dakota State University. “I think it has to do with grazing activity.”

The life cycle of Ostertagia ostertagi, the brown stomach worm, is pretty straightforward. Adult worms, living in the animal’s abomasum, produce eggs that are passed out in the manure. The eggs hatch in the fecal patty and the juvenile larvae wiggle up a nearby blade of grass and wait for another animal to come along and ingest them. Back in the animal’s stomach, they grow to adults and start the whole process over again.

“In normal situations, cows are pretty fussy,” Stokka says of their grazing habits. “They don’t normally eat right up next to a fecal patty.”

But when you have dry conditions and there’s less forage to eat, cows will eat pretty much everything, and the grass is greener next to a cow patty. “So some of the parasites may not last near as long once they hatch out, but because of grazing behavior, the risk of internal parasites actually increases during dry weather.”

That sets the cow and her calf up for several unsavory things to happen, says Phillip Kesterson, a Bridgeport, NE, cow-calf veterinarian. Internal parasites affect cattle two different ways, he says. One is that they reduce the animal’s appetite; the other is that they suppress the animal’s immune system.

“On a relative basis, with feed being short and animal condition being tough, there’s possibly a greater advantage to deworming now as opposed to when times are good,” he says. If you take a little away from an animal when forage is lush and plentiful, the animal can still flourish.

“But if you take a little away from an animal that’s already marginal, that’s a problem. Those parasites are taking a little bit away from that animal on a minute-by-minute basis; if feed quality and quantity is reduced, that’s bad.”

Cows, calves or both?

While worming the calves is the highest priority this fall, Kesterson and Stokka both agree cattlemen shouldn’t forget their cows.

“The calves, because of their age and because of what you want them to do, will undoubtedly give you the greatest return,” Stokka says. “The last thing we want to happen to that calf is that he eats less and might be under some kind of immunosuppression at a time when we’re trying to keep him healthy and wean him off the cow.”

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But the second priority is the cows. “Their nutrient requirements drop considerably (after the calf is weaned) but we want to clear up those internal parasites for the upcoming months,” Stokka says. “We want those cows back in a good body condition score so we can maintain them over winter with less feed.”

Beyond worming both calves and cows, Kesterson encourages cattlemen to take their worming program another step and consider doing a fecal egg count. It’s not an absolute detection tool, he says, but it still has some diagnostic value.

He ran some fecal egg count tests on his own cows when he preg-checked them in early August. He wormed them last spring and wanted to see what kind of parasite load they were carrying through the summer.

The counts came back zero. “I don’t believe that the cattle are parasite free,” he says. “I think it’s highly unlikely that we get rid of (the parasites) completely.” But he did use the results to plan his late summer and fall management options. Based on the results, he didn’t worm his cows at preg check, choosing instead to wait.

“We’ll come back this fall and make sure we not only drench the internal parasites, but have something to control lice and grubs. If you don’t address grubs, they will resurface. We’ll clean the cows out so we aren’t feeding those parasites during our most expensive feeding time, which is the winter feeding period.”

Early weaning

Somewhere around 70% of the nation’s beef cows are in areas that are feeling the effects of some degree of drought. Just as Southern Plains cattlemen did last year, many are considering early weaning. It’s a great strategy, Stokka says, because it lessens grazing pressure and gives the cows more opportunity, during a time of nutritional stress, to recover and begin cycling.

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That also means ranchers can work their cattle earlier in the year. “My caution would be, when it’s hot like this, make sure you do it first thing in the morning,” Stokka says. “Don’t add heat stress to their processing stress.”

In fact, he says, if you vaccinated your calves at branding and aren’t vaccinating prior to weaning, consider waiting a while after weaning to revaccinate and deworm if possible.

“Always keep in mind what’s best for that animal – what’s best for its ability to fight off the stress and the pathogens that want to enter when you go through the weaning process,” Stokka says. “There’s no sense piling on heat stress. Weaning those calves in a low-stress manner is the best thing you can do. And wait until a little later to process them.”

Deworm twice a year

Kesterson and Stokka agree that both a fall- and spring-worming program will pay in better cattle performance. Done strategically, a worming program will successfully interrupt the life cycle of the parasites, keeping infestations at subclinical levels.

That’s why they also recommend a spring dose of wormer. Worms will overwinter in cold country and oversummer in hot country; since no dewormer is 100% effective, parasite control is an ongoing effort.

In the spring, Stokka recommends turning the cows out on green pasture, then bringing them back in 4-6 weeks later for worming. “As soon as she hits the grass, she’s going to start picking up worms,” he says. If you can wait until the worms complete their life cycle, you can clean both the cow and the pastures.

But not everybody can re-gather cows after turnout and work them. So the traditional management program is to worm them before turnout. “I think it’s critical that people who are turning them out at the same time they process use a dewormer with some residual so you have some protection for a time,” Stokka advises.

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In Kesterson’s mind, strategic worming is important. “It seems to be a very good value,” he says. “The clients I work with who have the best overall results at the end of the year obviously do a lot of things right, but they’re typically also people who deworm. But people who seem to have the lingering, smoldering problems possibly have the opportunity to improve management practices, which may include deworming.”