Liver Flukes — An Increasing Problem in Cattle
The fluke life cycle explained, and how to mitigate their effects.
March 5, 2025
A photo of adult liver flukes. [Photos by James Hawkins.]
Liver flukes start their life cycle in tiny freshwater snails, but end up in the liver of grazing animals (cattle, sheep, elk and deer) where they grow, mature, and lay and pass eggs. Feces containing fluke eggs must land in water for transmission to snails. If the animal’s feces land on dry ground, the eggs die.
If they land in water and hatch, the immature flukes penetrate the soft foot of the snail, enter its body and start multiplying. They stay in the snail and grow, then emerge and attach to plants growing in the water and are eaten by grazing animals.
Cattle primarily get two types of flukes — the cattle fluke, Fasciola hepatica, and the giant deer fluke, Fascioloides magna. Cattle are an abnormal dead-end host for deer flukes, since the flukes can’t pass eggs. When those flukes mature, the cow walls them off in fibrous connective tissue.
Many areas in the United States and Canada have problems with cattle flukes — wherever there is habitat for the snails. Some areas have more problems with deer flukes because these parasites are endemic in the wildlife (deer, elk, moose, etc.) and get picked up by cattle. Deer flukes are more difficult to control.
Anne Rogers, veterinarian for Edson Veterinary Clinic, Edson, Alta., has seen many cases of deer flukes crossing from elk to cattle.
“We see flukes in cattle grazing low-lying areas and marshes, and see everything from cattle just not doing well to cattle that die of liver failure if damage is severe,” she says.
Cattle can also die from redwater disease caused by Clostridium haemolyticum when damage in the liver opens the way for this deadly clostridial infection.
“We recommend vaccinating annually with an 8-way clostridial vaccine that contains protection against redwater,” says Rogers. In some areas, ranchers need to vaccinate twice a year.
Any producer who experiences an unexplained death in their herd should request a postmortem exam, she recommends. “Otherwise, we won’t know what caused it or how to prevent more deaths.”
With the cattle fluke, feces can be checked for eggs. But deer flukes offer no good way to test and diagnose them in the live animal, says Rogers. These flukes get walled off in the liver and can’t pass eggs. The problem is generally not diagnosed until the animal dies or is slaughtered and the liver is checked.
Though some animals do poorly and lose weight, others seem healthy. “We’ve found deer flukes in 4-H steers that were fat and healthy otherwise,” Rogers says. The liver is full of flukes that haven’t done enough damage yet to create an adverse effect.
A liver damaged by flukes.
![Fluke eggs are passed by cattle in their feces. Cattle feces that land in water allow the eggs to hatch and find snails. [Photo by Heather Smith Thomas.]](https://cd.angus.org/-/jssmedia/project/american-angus-association/angus/angus-media/angus-beef-bulletin/abbx-articles/2025/03/hawkins-fluke-egg-s.jpg?mw=1440&iar=0)
Fluke eggs are passed by cattle in their feces. Cattle feces that land in water allow the eggs to hatch and find snails.
![Liver flukes begin their life cycle in snails. [Photos by James Hawkins.]](https://cd.angus.org/-/jssmedia/project/american-angus-association/angus/angus-media/angus-beef-bulletin/abbx-articles/2025/03/hawkins-snails-s.jpg?mw=1440&iar=0)
Liver flukes begin their life cycle in snails.
When deer flukes are in the wrong host, sometimes they migrate through the body instead of to the liver, Rogers observes. “I’ve found them in the lungs, creating an issue there.”
The typical treatment for cattle flukes is albendazole, which kills mature cattle flukes in the liver. But it doesn’t work as well for deer flukes.
“If we find a herd with deer flukes, we use albendazole in higher doses,” she says. “At necropsy (in treated animals) we’ll find dead flukes in the liver, so it does seem to kill them. There is no drug specifically labeled for deer flukes, however, so your veterinarian must prescribe the higher dose.”
To effectively treat cattle or deer flukes, work with a veterinarian regarding products, dosage and timing; you need to treat cattle at a certain stage of the fluke’s life cycle when they are susceptible to the drug. There are also precautions about using albendazole during the first trimester of pregnancy, Rogers mentions.
The main thing is to vaccinate at least annually for redwater. She cautions against irregular vaccination protocols, saying that in many regions, ranchers used to simply vaccinate young cattle for blackleg (using clostridial vaccine that also protects against malignant edema, etc.) and maybe revaccinate every few years. This may have worked back then, but in today’s environment, producers should vaccinate annually with the 8-way vaccine that also protects against redwater. This is a very inexpensive and effective vaccine.
It’s hard to say how prevalent deer flukes are in wildlife or how many hunters find damaged livers in deer, elk and moose they harvest; it’s a little easier to keep track of them in cattle. The local custom butcher lets her know when he finds a damaged liver.
“With veterinarians, ranchers and butchers working together, we get a better picture of what’s going on.” — Anne Rogers
“With veterinarians, ranchers and butchers working together, we get a better picture of what’s going on,” says Rogers.
Redwater is becoming more common; producers in certain areas must vaccinate.
“For instance, 20 years ago we didn’t have redwater in our practice area, but it’s steadily increased. Parasites move around with their hosts, and so do various diseases,” she says. Wherever there is snail habitat, there is potential for liver flukes, and wherever there are clostridial diseases in cattle, they may spread into new areas with movement of cattle. The flukes may already be in a certain area, and then the potential for redwater comes along (with dormant spores able to survive a long time in the environment) with the movement of feed and cattle.
Editor’s note: Heather Smith Thomas is a freelance writer and cattlewoman from Salmon, Idaho.
Angus Beef Bulletin EXTRA, Vol. 17, No. 3-A
Topics: Health
Publication: Angus Beef Bulletin
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