Our ram Harris has died

We found Harris dead in the field today. We try to take animal deaths as inevitable part of having animals, but it is always sad as you feel you failed them, and there are some you get more fond of than others. Harris was one we really liked. Sadly he is the second sheep to die recently with Skye (who was also a favorite) dying a few weeks ago with similar symptoms. They both suddenly got thin. Then they had diarrhea, then they died. One of the others (Tara) is also suddenly thin so we took her to the vet. The vet tested red blood count and she had low red blood cells suggesting worms (although we had wormed her only a couple of weeks ago). The vet gave us a different wormer (which covers tapeworm, roundworm and liver fluke as far as I can tell). Hopefully that will fix the problem - we are not sure what worm she thinks it is. My reading suggests our current wormer doesn't cover tapeworm.