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Weathering Parasites

Hurricanes and drought make for some interesting scenarios in 2006 parasite control.

Spring is the season of life. Some life you appreciate; some you don't.

No matter where in the U.S. you live, worms, flukes, flies and other parasites would fall into the second category. The level of concern you may have depends on where you live and the weather you enjoy.

Cattlemen in Louisiana and Mississippi will be forgiven if their level of concern about parasites this year takes a back seat to other issues. Nearly 20,000 cattle died as a result of the storms and floods caused by hurricanes Katrina and Rita, according to Jason Rowntree, Louisiana State University Extension beef specialist in Baton Rouge.

Another 10,000 cattle in each of Louisiana's Vermillion and Cameron Parishes were displaced due to the storms. About 170,000 cattle lived along the I-10 corridor in Louisiana and Mississippi, Rowntree says.

“Both storms together hit areas that even old-timers can't remember being hit,” Rowntree says. “It will be years before it gets built back up. It's certainly not going to be a short-term project.”

According to Rowntree, some salt water has come in and not gone back out. Still, cattlemen in the area are “hoping for green grass soon,” he says. “They'll be in good shape if they get a good green-up this spring.” And cattle “are still walking out of the marsh.”

What the storms mean for the parasite population in the area isn't totally known. John B. “Jack” Malone, DVM, LSU professor of veterinary parasitology, says a flood could dilute the parasite levels, though it depends on the circumstances.

“It's possible that [the storms] could have helped by wiping out all of the [snails that transmit] liver flukes,” he says. “A storm surge that flooded coastal areas of southwest Louisiana in the 1980s killed snail populations in fresh water habitats. They didn't return in major numbers until the next year.”

Malone says snails can't survive in more than five parts per thousand saline — about one-sixth of sea water levels.

The nutritional stress the situation is putting on the cattle is a key to potential parasite problems down the road, Malone says. “Any time there's nutritional stress, the parasite problem is going to be worse,” he says. “It's just fundamental that when there's overgrazing and nutrition problems, [cattle are] picking up worms,” and are more affected by them. Weather is definitely going to have an impact, he says.

Par for the course

About 650 miles to the east, veterinarian John Yelvington knows what he means. “When we get hot weather and a lot of water in Florida, it can be a problem,” he says. “That's why we have an ongoing parasite problem. It doesn't come and go as it might in some other parts of the country.”

Yelvington is a vet in Lake Placid, FL, about two hours south of Orlando in the central part of the state. He's been a practicing veterinarian for 25 years, the last eight as a beef and equine specialist.

Floods may present additional problems, Yelvington says, because they “might spread our parasites around to all areas of the pasture.” He notes some sections of the ranches will stay wet and present problems all year long since the parasites tend to thrive in warm, moist areas.

According to Yelvington, Florida cattlemen work the cattle in March to control the nematodes, then in late fall to control the liver flukes — which can be especially challenging in his area. Because of the large size of the herds, these efforts can last up to six weeks each season.

“Parasites seem to be evolving,” Yelvington says. “To get the best bang for the buck, cattlemen need to rotate families of dewormers.”

Yelvington also says there's no question cattlemen need to treat for parasites when they have the opportunity. “When I was getting out of school there was some discussion of whether there was a tolerable parasite load. That's been pretty much disproven in this area.”

A different problem

On the other side of the country, the weather problem can be the opposite, but the parasite problem is the same.

“Drought is a major factor in how bad a parasite problem can be,” says John Maas, University of California-Davis Extension veterinarian.

Maas says when cattle become concentrated on the land, grass will usually be shorter due to overgrazing, and there will be more fecal contamination and more eggs ingested. Mild winters — without freezes to kill the parasites, and with extra rainfall that contributes to moist conditions — are also considerations.

“Both situations play into the hands of the parasites, so to speak,” he says.

Maas agrees with Yelvington that while fecal tests would be best to determine a need for treatment, you're most usually better off not taking chances.

“We see parasites literally suck the weight off cattle,” Maas says. “It's almost always a money-making proposition to treat the animal, as the cost savings (from less weight loss) will be greater than the expense.”

Another way to lower parasite levels, Maas says, is to keep treated animals on clean land.

“One of the errors cattlemen make is they don't move cattle onto clean pastures after deworming them,” Maas says. “This encourages recontamination. Cattle should be moved to clean pastures within a week (of treatment).”

Walt Barnhart is president of Carnivore Communications LLC, Denver, CO, and a former communications director of NCBA.

Learning more

Understanding more about all of the facets of parasite control is the purpose of an upcoming study by researchers Arthur C. Linton and Doug Walsh, PhDs in Washington State University's Irrigated Agriculture Research Extension Center in Prosser.

Under a grant from USDA's Risk Management Agency, the duo is researching both internal and external parasites, the levels of infection and risks, economics of parasite management and other issues. The study is called “Reduced Risk Pest Management Strategies in Beef Cattle.”

“In the Southeast, there's no question internal parasites are a problem,” Linton says, noting that doesn't mean the same kinds of parasite management strategies are appropriate in Washington. He says Washington has a broad range of climates, from high rainfall on the West Coast, to desert in the south central area to colder and mountainous in the northeast.

“The situation will change from area to area,” Linton says. “Since there are only so many dollars to go around, we want to look at the economics” of parasite management in different regions.

According to Linton, cattle build immunity to some parasites as they age. While calves and younger cattle should be treated, it isn't necessary to treat all cattle — “at least not in all environments.”

TAGS: Parasites