It is worth reiterating that the worms sheep get from dogs
cannot be treated in the sheep. The
only way to control them is by worming the
dogs. We also pick up our dog poo, because in the countryside, dogs pick up worms from all sorts of carrion, rodents, etc, and even though we worm our dogs every three months as recommended for dogs in rural areas, that doesn’t stop them getting reinfected within the three months after they ate a dead rabbit the day after you wormed them
The dog worms create cysts in the sheep. Often there are no clinical signs, and you don’t know anything about it until you get some of the meat condemned with tenuicious cysts. Sometimes the cyst is somewhere it causes a problem - could be blindness, or fits, respiratory issues, etc - but unless you get a post mortem you wouldn’t know the cause.
When you see tapeworm segments in the sheep’s poo, that isn’t the worms they get from dogs. That’s the sheep tapeworm, which has the pasture snail as its secondary host, and doesn’t really cause the sheep or you any problems - except that the sheep need to eat more, as they have to feed their tapeworm as well as themselves.