Jim Sitz can't take any chances on compromising the productivity of his cow herd. With ranches in Dillon, Jackson and Harrison, MT, Sitz Angus Ranch has a reputation for providing high-quality Angus seedstock to the U.S. cattle industry.

There are a lot of management factors and details beyond the gene pool that he and brother Bob take very seriously in raising seedstock. Jim, who manages the Dillon-based farming operation and the Jackson (Big Hole Valley) ranch, first got concerned when he saw liver fluke infestations cropping up in area commercial herds.

Several of Sitz's neighbors found liver flukes in their cattle, and local veterinarians recommended treatment after autopsies revealed heavy fluke loads. The Sitzes began treating cattle for liver flukes at their Big Hole Valley ranch in 2002.

“We've never seen liver flukes in our cattle and, especially in these years of mild winters, it's hard to tell how much difference fluke treatment has on our cows,” Jim says. “But, we're convinced that we're preventing a problem before things like weight loss and lower conception rates take a toll — things we can't afford to let happen.”

A beef quality issue

The common liver fluke (Fasciola hepatica) is endemic to 26 states and has been associated with lower weight gains and poor feed conversion in untreated cattle. Liver flukes also adversely affect reproductive hormones when they infect the animal's liver, leading to delayed estrus in heifers.

The 2000 National Beef Quality Audit, conducted by Colorado State University, Oklahoma State University and Texas A&M University in U.S. packing plants, ranked liver-fluke infestations as a top-10 beef quality issue. The audit found 24.1% of U.S. cows and bulls had liver flukes at slaughter.

“The only way to really know if cattle are infected with liver flukes is by inspecting the liver at slaughter or by running a fecal examination,” says James Hawkins, DVM, Merial Veterinary Professional Services. “Fluke infections can vary annually. If cattle are of unknown origin, there's no traceback reference to solve the problem at its source.”

Gary Zimmerman, Livingston, MT, DVM, isn't surprised Sitz initiated a treatment regime for liver flukes. A veterinary parasitologist and president of Zimmerman Research, a firm that conducts independent research for the animal health industry, Zimmerman is also a leading national expert in bovine liver flukes.

“In many areas of the Western states, liver flukes are endemic — they're common just about every year,” he says. “This is also true for the Gulf Coast and even into parts of Missouri and Kansas.”

Right time, right stuff

Knowing flukes are a potential problem for many ranchers, Zimmerman is concerned ranchers like Sitz are treating for liver flukes at the right time with the right product.

Treatment depends on the transmission pattern of the fluke, which can vary year to year due to environmental conditions. Generally though, transmission begins in late July and runs into October.

“Cattle grazing during that period can pick up flukes,” Zimmerman says. In eight to 12 weeks, the flukes become fully mature.

This period of ingestion and subsequent fluke maturity is important in determining control measures, especially for compounds labeled for “mature” flukes.

“Classically, the research says it takes about eight weeks from infection until the parasite matures to the point of passing eggs,” he adds. “But, this maturation period can be highly variable.”

Two drugs available in the U.S. for treatment of F. hepatica liver flukes are clorsulon (Curatrem® and Ivomec Plus®) and albendazole (Valbazen®).

Research literature indicates clorsulon is very effective against adult flukes and somewhat effective against later stages of immature migrating flukes. Albendazole is effective only against adult liver flukes.

If your animals have been infected during late July through mid October and you treat them in late October and November, the maturation level of the infection may not be adequate for removal by compounds labeled for mature flukes.

“The later in the year you treat, the more chance you have of killing more flukes,” Zimmerman explains. “But, timing of treatment has to be balanced with continued damage flukes are doing to the animals.”

Sitz appears to be doing it right. He says they treat their cows, calves, heifers and bulls when working cattle in late November. His cost of treatment with Ivomec Plus (ivermectin/clorsulon) is about $4.50-$5/head — but, it also works on other internal and external parasites. Zimmerman's “double-blind” data shows this treatment can result in up to $15-$20 in increased animal productivity.

Another problem fluke

While treatment can kill the flukes in an animal and help restore productivity, liver damage can't be reversed. The presence of one fluke is cause for condemnation of the liver.

“The liver is going to have lesions and it cannot be used for human consumption,” Zimmerman adds.

While F. hepatica in cattle isn't considered a problem in many Midwest areas, Fasciola magna is found throughout North America, primarily in deer, its natural host. This fluke infected nearly 100% of the livers from calves raised in the Upper Peninsula of Michigan that were entered into the Michigan Beef Improvement Program.

Dan Grooms, DVM, Michigan State University College of Veterinary Medicine, says, besides liver condemnation, F. magna appears to cause few, if any, disease symptoms in cattle.

“However,” he says, “little is known about the effects this parasite may have on production efficiency.”

In contrast, F. magna infection is highly fatal in sheep and limits sheep raising in areas heavily infested with the parasite. In limited studies, both albendazole and clorsulon appear to be less effective at eliminating F. magna infections. Although there is no specific supporting evidence, treatment of pastured calves or yearlings when entering the feedlot may be of benefit in reducing liver condemnation and improving performance.

“Cattle are a dead-end host for F. magna,” Grooms adds. “This creates a problem in detecting cattle with F. magna as most parasitic diseases are diagnosed by identifying eggs in the feces of infected animals.”

Counting eggs, finding flukes

Zimmerman agrees that, outside of post-mortem examination of an animal's liver, diagnosis of liver flukes is difficult.

“The routine floatation technique a veterinarian might offer for counting parasite load doesn't recover the eggs of the common liver fluke,” Zimmerman says. “When put into solution, fluke eggs won't float, and thus can't be counted.”

There have been attempts to develop microscopic screens to capture fluke eggs, but nothing is yet commercially available. Zimmerman developed a rapid serologic card test for flukes several years ago, but it also is not commercially available.

He says many times ranchers find they have a fluke problem only after harvesting an animal for their own use. Such is the case with one Wyoming rancher.

“After butchering several of our animals, we found them infected with liver flukes,” says Ken Shriver, Pinedale WY. “You can't tell by looking at the cattle, but once we saw the flukes in the livers we knew there was a problem.”

In 1989, Shriver received a call from a feedlot that had purchased his yearlings.

“The feedlot had some problems with cattle performance,” Shriver says. “At harvest, they discovered an abnormally large amount of cattle infected with liver flukes.”

His veterinarian recommended he treat cattle for liver flukes with a broad-spectrum endectocide that controls liver flukes. Today, he's pleased with the results.

“The biggest problem for ranchers like this is getting an actual diagnosis for liver flukes,” Zimmerman explains. But, he says, ranchers who work with their veterinarian to diagnose and successfully treat liver fluke problems can expect a return on investment of $1.25 to $1.50/dollar spent on treatment.

There are few other areas of animal health where ranchers can gain the kind of increased overall productivity that result in such improvements in profit.

“In many areas of the West, you can assume many of the animals are going to be infected,” Zimmerman says. “And, fluke treatment is probably going to be indicated.”