With pastures so wet and grass a little short early in the growing season, producers should be watching for signs of liver fluke infections, said David Fernandez, Cooperative Extension Program livestock specialist at the University of Arkansas at Pine Bluff.
While rarely fatal in cattle, flukes can cause death in small ruminants. Liver flukes reduce the value of a carcass thus lowering prices producers receive, he added.
Liver flukes are flatworms that invade the liver of livestock and cause liver damage. Liver flukes have a two-host life cycle. The eggs only hatch in water, so in wet years like this one, there are more problems with flukes, Fernandez said. The larvae infect a snail where they develop and reproduce asexually. The larvae then exit the snail and encyst on nearby vegetation. When livestock eat the vegetation, they become infected.
The larvae migrate through the wall of the small intestine and into the liver. There, they tunnel through to the bile ducts. They damage the liver and can cause liver abscesses, a distended and painful abdomen, anemia and sudden death in sheep, he said. In lower numbers, they often mimic the signs of a barber pole worm infection. Flukes can also cause bottle jaw, poor condition, weight loss, fatigue and lower milk production.
Cattle, on the other hand, may be heavily infected yet show no signs of disease. Cattle develop partial immunity within about five to six months, but sheep do not, he said. Instead, sheep accumulate more and more liver damage and eventually die.
Mature flukes live in the gall bladder or bile ducks where they damage tissue, consume blood and lay eggs. The eggs pass into the intestines with the bile and are deposited in the feces, starting the cycle again.
Fernandez offered the following tips on reducing liver fluke infections:
- Keep livestock out of areas where water accumulates
- Avoid pasturing animals in areas with snails in the grass
- Mow pastures to remove cysts as encysted fluke larvae can remain viable for months if they do not dry out.
Treatment options include clorsulon, found in Ivomec Plus dewormer, and albendazole (Valbazen) in the United States. Treat animals before the rainy seasons begin, such as fall or late spring in Arkansas. This can help reduce the number of eggs laid on pastures and reduce the chance of infection, said Dr. Fernandez. Be sure to follow label instructions as Valbazen should not be given to pregnant animals. Neither Valbazen nor Ivomec Plus is labeled for use in lactating animals. Both have long withdrawal periods before slaughter.