This is one chapter of a wider and more confusing story, but I'll do my best!
We have a few of this year's lambs which haven't been putting on weight and have been very squitty for some time. This has happened the past few years and despite trying all sorts of things like vitamin drenches and boluses we've never really gotten to the bottom of it.
So, as an extra check, I had an FEC done two weeks ago on a sample from the worst affected. This came back with a mixture of nematodirus and strongyle eggs at 300 epg. We then wormed with a group 3 ML wormer (Molemec ivermectin) and retested him two weeks later. This new sample has come back with 150 epg, and all nematodirus.
So now both the vet and I are confused. Shouldn't the wormer have knocked out the nematodirus also? My understanding was that the one good thing about nematodes is that they haven't figured out how to resist wormers yet (hence why we use white wormers against them specifically, even though they're not much use any more against most other types of worms).
I'm still working through this with the vet, but in the meantime, does anybody have any ideas?