In the hierarchy of internal parasites in beef cattle, there’s little doubt that the nematodes (Ostertagia, Cooperia, etc.) are the headliners. But there’s an ambitious understudy – liver flukes – inching their way into the spotlight.

It wasn’t that long ago that flukes were essentially concentrated on the moist Gulf and Pacific coasts. Due to the modern movement patterns of cattle, wildlife and hay, however, flukes are now found in 26 states. In fact, a recent National Beef Quality Audit found that 24% of U.S. cattle had liver flukes at slaughter, resulting in liver condemnations that cost millions of dollars annually.

 The U.S. can boast of three species of flukes. The cattle fluke (Fasciola hepatica) is the most widely distributed, according to James Hawkins, a Jackson, MS, DVM and consultant for Merial. Then there’s the deer fluke (Fascioloides magna), and the lancet fluke that exists in New York, Maine and Eastern Canada.

Flukes depend on a small snail for an intermediate host. Tom Craig, Texas A&M University veterinary pathobiologist, says cattle ingest these parasites as cysts attached to plants consumed in or near water. Tiny flukes are released from the cysts during digestion, which penetrate the gut wall and migrate to the liver, where they feed – and destroy tissue. They then migrate to bile ducts to grow into adults and lay eggs.

The eggs travel with the bile into the cow’s gastrointestinal (GI) tract and are passed in manure. Feces containing fluke eggs must land in water in order for the eggs to hatch into free-swimming miracidia, says Floron (Buddy) Faries, Jr., DVM, Texas AgriLife Extension. If the manure lands on dry ground, the eggs die.

The eggs will hatch in about 30 days if the water temperature is above 55°; and the tadpole-like miracidia immediately begin swimming in search of a snail host. Upon penetrating the snail, they spend two months propagating, after which they emerge again as swimmers to attach to a plant growing in water, to be eaten by a cow.

“Wherever there’s standing water, snails will be present when weather warms up in the spring. If flukes come out of the snail in July, however, the water may not be there, and this will break the life cycle,” he explains.

“If there’s three months of water – one for eggs to hatch, and two months to develop in the snail – flukes emerge and encyst on grass. After that, the water could dry up but the flukes will still be there, waiting on grass plants. Cattle might eat that grass, or it could be cut for hay, and flukes get into the cattle that way,” Faries says.

Swamps can be fenced off to keep cattle away from flukes, “but when feed is short in a drought, this may be the only green place on the farm,” Hawkins says. Thus, some producers end up with high levels of fluke infection during a drought because cattle are grazing wet areas they don’t normally graze.

All species of flukes can kill cattle, but deaths are rare. “Generally we see chronic, slowly developing disease that reduces weight gain or affects overall animal health. Cows become poor doers and eventually get culled,” Hawkins says.

Liver damage opens the way for clostridial bacteria that cause redwater disease. With liver damage, the immune system is also compromised, increasing susceptibility to disease and diminishing ability to respond to vaccine or antibiotics.

“Liver damage affects everything the body needs to do in converting nutrients into utilizable proteins, energy, vitamins, etc. Liver flukes affect gain in young cattle, but this is usually a slow-developing problem compared to the effect of worms,” Hawkins says.

“Any time an animal dies on your place, check the liver. If there is severe damage, you can see it, and you’ll know you have flukes,” he says.