There is no definitive and confirmed evidence in scientific literature that tapeworms (Moniezia sp.) cause any ill effect to sheep or that removing them gives a beneficial effect. Folklore blames tapeworms for all manner of problems, but none of it is substantiated.
Tapeworms (Moniezia expansia) have what is known as an indirect lifecycle. To become infective to sheep or goats, the eggs need to first be eaten by a mite that lives in the soil or on pasture. These mites are more active during the summer months. To complete the life cycle, mites containing tapeworm eggs are eaten by sheep/goats.
The mites get digested in the animal's gut and the eggs are released to go on and develop into adult tapeworms in the animal's gut. The preferred site of adult tapeworms in the sheep is the small intestine, where it attaches to the inner surface using strong, muscular suckers found on the head of the worm.
Tapeworm segments can be visible in the feces, with a white rice grain-like appearance. Adult worms, often up to a meter or more in length, can also be seen on post-mortem or, when expelled, as passed in the environment, typically in yards or other areas where sheep and/or goats are concentrated. Tapeworm eggs in fecal samples can be detected using the standard worm egg count procedure.
It is not possible to justify the treatment of sheep solely for tapeworm as there is no definitive and confirmed research that shows tapeworms have any negative impact on sheep even very young lambs. If you feel you must remove tapeworms, use a drench containing praziquantel. Albendazole (Valbazen®) aids in the removal of tapeworm segments but will not kill the head of the worm.
Source: Australian Wool Innovation LTD (wormboss.com.au)