Lucky in Water, Unlucky in Liver Flukes

If you're lucky enough to have standing water and wet pasture conditions, then be on the lookout for liver flukes in your cattle.

Cattle in the U.S. can get 2 types of liver flukes - the cattle fluke, Fasciola hepática, and deer K fluke, Fascioloides magna. The cattle fluke is * most common and most widely distributed, ac* * to Dr. James Hawkins, consultant for * Merial Animal Health, Jackson, Miss.

"The deer fluke can be very difficult to I control in cattle. Both species of flukes can kill cattle, but it is unusual to see cattle fluke actually killing cattle. Most of the time, we just see chronic slowly-developing disease that reduces weight gain or causes weight loss and reduces overall animal health. Cows can become poor doers and eventually get culled," says Hawkins. Flukes damage the liver, which may set up cattle for other problems, such as redwater disease.

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

Compare liver fluke damage to worm damage

Researchers at the Louisiana State University Experiment Station, Alexandria, sought to discover whether worms or liver flukes are the most important internal parasite in cattle. What happens if cattle have both?

Researchers took weaned beef replacement heifers from other university farms to breed and send back as bred heifers.

The heifers were divided into 4 groups of 24 head per group. "One group was treated with injectable ivermectin - to kill GI [gastrointestinal] tract nematodes and nothing else," says Hawkins. Another group was treated for liver flukes only. Another group was treated for worms and flukes. The fourth group served as untreated controls.

"They did this for many years, but the initial study was for 4 years. Dr. J.C. Williams and Dr. Loyacano published the results," Hawkins says.

In young cattle the GI nematodes have the most profound impact on gain, the research shows. "These cattle were on pasture and in winter were on planted ryegrass, supplemented by corn-based concentrate ration so they would gain a pound per day, to reach breeding weight," he explains.

The dewormed group gained an average of 23 to 25 pounds more than the control group, "which actually did pretty well, gaining approximately 1 pound per day." Hawkins says the untreated group gained 53 pounds, which was "more than necessary to be at their proper weight at breeding." Due to the extra 23 to 25 pounds gained by the dewormed group, "that group could have been backed off a little on feed and still attained breeding weight, which would have saved money," says Hawkins.

The group that always did best, in all the years of the study, was the group receiving both treatments - worm and fluke control. "They had better weight gain and increased conception rates," he says.

For this study the cattle were naturally infested on pastures known to have liver flukes and worms. During their growing period, under these conditions, the worms were a lot more important than flukes in terms of affecting weight gain.

"But if a producer sees signs of heavy fluke infections, this could be a different story. I've seen several instances in which young cattle died on pasture from liver failure, so people need to be aware of this possibility," he explains.

Flukes affect conception rate

In the Louisiana study comparing worm impact and flukes, heifers were bred by artificial insemination (AI) after the growing period.

"The interesting thing was flukes had a big impact on conception rates. Even though the untreated control heifers were at proper weight at breeding, the conception rate was dramatically reduced - to the point that Dr. Loyacano wondered why these heifers didn't get pregnant like they should. So they decided to keep that group and follow them all the way through calving, to try to see what was going on," Hawkins says.

"The untreated heifers not only had low conception and calving rates, but there was also a significant reduction in birth weight in their calves. One calf weighed only 26 pounds and did not survive.

"What I'd been taught in veterinary school is that conception is primarily dictated by body condition and proper weight at time of breeding. So I did a complete literature search and talked to other parasitologists.

One person, trained in human parasitology, mentioned a human fluke that in other parts of the world can affect normal development of the gonads, especially if it infects young boys."

Hawkins also found a study in Spain where a theriogenologist had experimentally infected dairy heifers with liver flukes.

"He had an uninfected control group and monitored everything, including conception. He found that flukes impacted the estrogen-progesterone ratio in the heifers. Their estrogen was too high. You would tend to worry about estrogen being too low, but what happened was the progesterone was lower than normal and estrogen was higher than normal. In his study, the fluke-infected heifers were 39 days late, on average, coming into their first standing estrus, and their conception rate was also statistically lower."

The ratio of estrogen and progesterone is important for conception, rather than the actual levels, except there has to be a certain level of progesterone or pregnancy won't be maintained after the animal conceives.

"In the fluke-infected heifers, the ratio was messed up, interfering with heat cycles. This researcher felt that the low progesterone could cause the animals that did get pregnant to lose the pregnancy," says Hawkins.

"Herds with chronic liver fluke infection could have problems with reproduction. I've seen this in herds along the Gulf Coast, such as in south Louisiana and southeast Texas.

"Some producers there feel that a 75 percent conception rate is the best they can do. I always attributed this to things like poor management, heat stress, poor nutrition, etc., but it may be because, even though they are treating for liver flukes, they aren't getting enough control to alleviate this effect. This has not been confirmed with studies in beef cows; it was just confirmed in dairy heifers. I believe it probably happens in adult cows, to a lesser extent," he says.

Flukes affect bull fertility

There is also data from Texas A&M University showing fluke infection was the only thing that statistically correlated with a bull failing his breeding soundness exam.

"This study was done with several thousand bulls over 9 years of breeding soundness exams," says Hawkins. The results indicated that if bulls failed their exam and had a positive test for flukes and were treated for flukes, they would almost always have a successful breeding soundness exam 6 weeks later. This was especially important in young bulls."

OSU studies flukes' effect on feedlot cattle

In a feedlot situation, flukes can be a problem. A number of studies show that gain and feed conversion are affected. "Gain is primarily affected by number of flukes - the more flukes, the more impact. But the effect on feed conversion is probably the most important, because of the price of feed. If it costs you more to finish that animal than normal, you lose money," says Hawkins.

"The best study I saw on this was done by Oklahoma State University, monitoring individual animal feed intake and gain on a group of steers. When they went to slaughter, each liver was checked for flukes. Then the researchers went back to see what each animal did on average daily gain and feed intake. They found that flukes significantly impacted gain and feed conversion," he says.

"It definitely pays to control flukes, but in the feedlot it's difficult to diagnose fluke infection and relatively expensive. The fluke eggs are hard to find. You have to use a special technique. Even if you find them, this doesn't indicate whether there is a significant enough level of infection to make a difference," says Hawkins.

"So we recommend that feedlots getting cattle from fluke-endemic areas treat them, just for insurance. Even if you get only 1 group out of 10 with a problem, it will pay to treat them all.

"Using a product that gets flukes is not that much more expensive than using a product that doesn't. The problem today is that cattle are moved around a lot. You may not know where they originate unless you are buying cattle from the farm or ranch on which they were raised and know the source," he explains.

Treating for flukes

Two products will kill liver flukes: IVOMEC-PLUS and VALBAZEN. "To get deer flukes you need to use 2 to 4 times the recommended dose for cattle flukes. Even then, you don't always get the effect you'd like.

"Deer flukes are inherently resistant to the drugs. Cattle are an abnormal host for deer flukes, so the animal walls them off. Once the deer flukes mature and become adults, they pair up in the liver and become stationary. At that point the cow treats it as foreign and walls it off with a fibrous connective-tissue capsule, like an abscess," Hawkins says.

"Because of the fibrous capsule surrounding the flukes, drugs can't touch them. So cattle are a dead-end host once these flukes are in the liver. They cause a lot of damage, however, before they get walled off. All we kill, when treating deer flukes, are the migrating immatures," Hawkins explains.

"In contrast, what we kill when treating cattle liver flukes are the adults, and not the immature forms." Killing adults prevents passage of eggs back into the pasture and thus breaks the life cycle, so there won't be as many immature flukes picked up by snails.

"Basically the only way to control deer flukes is to control deer, which is difficult or impossible. We are searching for new ways to control deer flukes. There are products available elsewhere in the world, but we may never have them here because most of them are carcinogens," says Hawkins.

At this point deer flukes are not as widespread as cattle flukes. "We find deer flukes along the Gulf Coast in certain parts of Texas and Louisiana. We also see them along the Great Lakes, such as Minnesota, Wisconsin, and a few in North Dakota," he says. To know whether deer flukes are a problem in your area, contact the state diagnostic lab and ask if they ever see deer flukes in necropsies, and where, advises Hawkins.

"With deer populations expanding, deer flukes are also expanding their areas. The same is happening with cattle liver flukes. We have ranchers contacting us who thought they never had flukes before but have them now," says Hawkins.

Timing of treatment for cattle flukes is important. It will be different in different regions. "If people know they have flukes they should treat twice a year. Any time an animal dies on your place, get it necropsied or open it up yourself and check the liver. If there is severe damage, you can see it," Hawkins says.

For treating cattle flukes, you need to know the life cycle of flukes in your area and how long it takes for immature stages to become adults.

"Transmission season is when it's wet. Treat cattle 8 to 12 weeks after the height of transmission season. When conditions begin to dry, treat about 8 weeks later. Some areas have some transmission yearround, such as Florida or South Texas. Your strategy there would be to treat for flukes each time you deworm," says Hawkins.

"Pay special attention to replacement heifers and young bulls. If you are not sure about flukes on your place, at least 1 deworming per year [with a product that kills flukes] for the cow herd is a good idea, and probably 2 for the replacement heifers - just to make sure they are gaining and producing to their potential and to save on feed costs."

Wherever there's standing water, snails will be out when weather Warms up in the spring. The eggs are passed in manure when cows wade in the watef, -hatch in aBbut 3 month and find a snail to develop in for 2 months.

Timing of treatment for cattle flukes is important.

Gain is primarily affected by number of flukes - the more flukes, the more impact.

In the flukeinfected heifers, the estrogenprogesterone ratio was messed up, interfering with heat cycles.