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Blood Suckers

St. Croix Fights Back

by AlanHarman

West Virginia University assistant professor Scott Bowdridge.
(Photo by Lindsay Willey)

West Virginia University assistant professor Scott Bowdridge.
(Photo by Lindsay Willey)

Last year the outlook seemed bleak regarding one all but unstoppable sheep parasite. “They’re becoming resistant to every drug on the market,” said West Virginia University assistant professor of food animal production Scott Bowdridge. “It’s a huge, huge problem.”

Haemonchus contortus, also known as red stomach worm, wire worm or barber–pole worm, is responsible for anemia, bottle jaw and death in infected sheep.

Bowdridge thinks there’s an answer in the St. Croix hair sheep. Last year the U.S. Dept. of Agriculture’s Nat’l Institute of Food and Agriculture (NIFA) funded some research of this idea.

Problems began in the 1960s. Drugs effective on barber–pole worms hit the market. Growers then paid less attention to resistance as a control method. Then, the drug Ivermectin came out in the early 1980s. Growers misused it, not killing 100 percent of barber–pole worms in sheep’s stomachs. Worms with natural resistance survived breeding up a newly resistant next generation.

Conventional (mostly–British) breeds don’t fight the worms as aggressively. No matter how many times they get the parasite, their immune response doesn’t improve until they get much older.

“Barber pole worms never developed a resistance to the St. Croix breed like they have to the drug,” Bowdridge says. “The St. Croix can clear themselves in five weeks after infection. They throw everything they have at it.”

The St. Croix, also known as the Virgin Islands White, is believed to have descended from hair sheep from West Africa. Some think it’s a cross of the Wiltshire Horn and the native Criollo.

Back in 1975, 25 Virgin Islands White sheep—22 ewes and three rams—were selected in St. Croix and imported into the U.S. by W. C. Foote of Utah State University. These sheep were the basis of the present St. Croix breed in the U.S. Ewes average 119 pounds, while rams average 163 pounds. Lambing rate varies from 150 to 200 percent—two lambings a year aren’t uncommon.

Bowdridge says the St. Croix breed developed under constant exposure to parasites. This exposure resulted in a super–charged immune response to barber–pole worms.

“Unfortunately, the St. Croix has little to no ‘commercial’ value in the U.S.,” he says. Breeds like Suffolk, prized by conventional U.S. growers, are relatively helpless to barber–pole worms— especially true when raised on grass. As “grass–fed” and “organic” lamb and wool demand rises, so does the threat of loss.

One avenue Bowdridge is looking at is cross–breeding St. Croix with commercial breeds to see if their strong immune system passes down to their offspring.

He’s also searching their genes to find what gives such robust immunity.

“St. Croix sheep launch an immediate, very aggressive attack on any parasite that enters their system, and you don’t see that response in commercial breeds,” he says.

Bowdridge is also looking for chemical and protein signals in St. Croix sheep that trigger the response. Once he finds this, he hopes to then develop a way to “awaken” other breeds’ immune response.

Bowdridge is now in the third year of raising and studying St. Croix sheep on WVU’s Animal Science Farm in Morgantown. The farm has 50 sheep for research on the worms: 25 commercial crossbred ewes and 25 St. Croix provided by colleagues at Virginia Tech. They’ve been raised and studied at WVU’s raised–floor sheep facility.

On pasture, barber–pole worms spread from sheep to sheep through worm eggs in the dung which hatch on pasture. Larvae crawl up the grass, which sheep then eat.

WVU researchers prevent new infections by keeping sheep on raised metal floors. “All their feces fall through the floor,” Bowdridge says. The raised floor lets him (along with graduate and undergrad students) control parasite exposure, better monitoring the animals’ response. He’s also working with WVU’s Organic Research Project.

Once Bowdridge finds the mechanics of the immune response in St. Croix, he hopes to work with private industry to develop dietary supplements that will trigger a similar boost in commercial sheep. He’s working to secure private support for ongoing research and product development, to supplement the seed funding from the NIFA.

Barber–pole worms live in sheep’s fourth stomach (the abomasum). Females may lay 10,000+ eggs a day; the worms vora­ciously suck blood from the stomach lining. A burden of 1,000 worms may remove nearly two ounces of blood a day from a sheep. Sheep heavily infected with barber–pole worms lack stamina, have pale gums, eyelids and whites of eyes and may get bottle–jaw and/or constipation. Infections cause big losses worldwide. The parasite has now adapted to cold–winter nations—scientists from Britain and Scandinavia report serious problems now. They were once only found in warm humid regions.

These St. Croix hair sheep may hold the secret to protecting their commercially viable cousins from deadly parasites. (Photo by Lindsay Willey)

These St. Croix hair sheep may hold the secret to protecting their commercially viable cousins from deadly parasites. (Photo by Lindsay Willey)

Until a parasite solution is found, Bowdridge says, keep using medications and only on sheep with bad infections. As the worms make sheep anemic, he says to wait until an animal’s lower eyelid goes from blood–red to very light pink or pale.

“Those are the ones we want to treat very quickly,” he says. “You’re only treating the animals that need it.”

Editor’s note: Growers can also breed St. Croix sheep. If consumers like it, it may fight a 50–year decline in U.S. lamb–eating, still taking place with our conventional breeds.

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