Generally if the deworming program can control Haemochus the other roundworm will be controlled as well. Young growing lambs are particularly susceptible to roundworms and should be dewormed when they are 3 to 4 months old. Tapeworms do not do as much damage to sheep as roundworms. The greatest concern is that if large numbers of worms are present they can physically block the intestinal tract and cause death. Flukes invade and migrate through the liver.
Sheep are very sensitive to flukes and even one fluke can cause enough damage to kill a sheep.
The life cycle of flukes requires a snail intermediate host. Therefore fluke problems are found in areas of standing water. One species of fluke, Fasciola magna can also infect deer and is a serious problem in northern Minnesota and Wisconsin. If you deworm sheep and turn them out in an infected pasture they will be reinfected with worms in 30 days. Plan your deworming to coincide with pasture rotation.