I deworm every quarter (4 times a year) and even so have lost 4 lambs in the past week. Had my suspicions confirmed by the vet today. They are full of Strongyles. Lately I've used Fenbendazole feed thru to deworm, but apparently I need to rotate to Ivermectin for a couple cycles. My problem, other than the obvious, is that I haven't found a feed thru version of ivermectin or Strongid that's designed for sheep.