David Pugh

A more passionate dissertation on worms has never been given than David Pugh’s presentation during Kansas State University’s Beef Stocker Field Day in Manhattan.

Pugh’s poll of the audience revealed the producers in attendance fell soundly into two camps — either they believed their pastures had too much of a worm problem or none at all. Regardless of the perceived problems, Pugh said parasite presence and resistance is not something the Midwest can continue to avoid.

As an Alabama-based parasitologist and cattleman, Pugh’s experience with de-wormers goes beyond his clinical studies and into the pastures themselves. With less pasture ground, more intensive grazing and warm, humid weather, the southeastern United States is a perfect host environment for parasitic pasture worms — a problem Pugh said could be traced back to the Civil War

“My experience in the Southeast is that we lost the War Between the States, smart people died and y’all got best choice up here,” Pugh said. “Y’all won lots of pastures, beautiful bluestem, lots of grasses, and we picked parasites.”

From a herd health standpoint, Pugh said parasite control is his No. 2 concern with nutrition being his No. 1. In stocker operations, those two can be at odds with each other.

“Internal parasites all live part of their life cycle in fecal material and in the pasture,” Pugh said. “The pasture is both the source of great nutrition and the source of most disease.”

More cows and more feces in a smaller area is a recipe for worm production, Pugh said. A small perimeter around dung piles in pastures becomes a hotbed for parasite production and propagation.

“They cannot complete the life cycle and can’t freely feed until a calf comes along and eats them and swallows them when they’re on the grass and then the digestive enzymes in the stomach, the abomasum, will digest the cuticle around the worm larvae,” Pugh said. “Now they can infect the calf and that’s important because if it’s dry and hot for a while these parasites don’t survive very well.”

By the time cattle display internal parasite symptoms from a loss of appetite to a dull hair coat, Pugh said the damage both physically and economically has already been done. Appetite and protein loss are two of the most detrimental results from the presence of parasites.

“Appetite suppression is the most important thing that internal parasites do,” Pugh said. “That’s paradoxical because it seems like if you’re feeding on a host you would want it to eat more.”


Like many medical marvels, the more a dewormer is used, the less effective it becomes and overtime resistance can build. For Pugh, this problem stems from a variety of misuse and poor practices.

“We have worms in sheep and goats that nothing will kill,” Pugh said. “We have some species of Haemonchus in cows that you can pour Ivermectin on it and hit it with a ball-peen hammer 22 times, and it will look at you and grin.”

Using generic wormers with less than 90 percent efficacy and releasing calves into clean pastures shortly after deworming are two of the biggest offenses Pugh identified in developing a successful deworming protocol.

“You’ve got to have a strategic deworming program,” Pugh said. “You have to design a herd health program based on that individual farm.”

While parasites are a very localized problem, Pugh identified two species of worms he’s most concerned about developing resistance in his research.

“The two biggest parasites we worry about are Haemonchus and Cooperia,” Pugh said.“Cows become immune to them really effectively by the time they are 2 years of age.”

Most problems with Haemonchus spp. and Cooperia spp. can be found in calves, replacement heifers and second-calf heifers, Pugh said. Deworming older cows year after year for these species in particular may be unnecessary and primary concern about control should be shown to calves with low immunity.

“Avoid deworming adult cows going into the summer,” Pugh said. “Treat replacement heifers differently than stockers or you will develop a point source of Cooperia in your brood cow herd.”

Pugh encouraged producers to look for early, subtle signs of worm problems in stocker cattle before the issue becomes more apparent. Recognizing slightly lower than expected gains could make a difference in both lost profits and in developing a bank of worms in pastures frequently used for stockers.

“You might buy calves from multiple local sources that have different management styles of controlling internal parasites but the worms they bring come for free,” Pugh said.“You can bring in parasites that are resistant to that certain kind of wormer.”

Avoiding using the same wormer on the same pasture year after year and avoiding pour-on wormers, especially generics, could greatly improve herd health for stocker operations.

“Pour-ons are poorly absorbed,” Pugh said. “We do not recommend using pour-ons of any brand anymore — and I’m not the only parasitologist to say that.”

Reading labels and investigating worming options fully can help producers not only control their parasite loads more effectively but could also help slow resistance development, Pugh said.

“Worms adapt. They improvise. They overcome,” Pugh said. “They figure out ways to whip the dewormers.”

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