OK. We moved into this property late December 2014.
We built 2 separate paddocks (boys and 1 set of mares - swapped out Sr/Jr), a pen made from the steel round pen panels & started the round pen (tho didn't get it finished until much later).
SPRING 2015 - the SR mares had been moved into the mares paddock when it was completed in February(I think?). In March, the two oldest - Bell & Bit were found to have a heavy infestation of lice. I treated EVERYONE in the paddock - tho I don't remember everyone having them. I treated all the brushes/combs/picks from their shelter. There are pine trees in their paddock. I know they were rubbing.
None of the other ponies had them, that I remember, in 2015 (or am I wrong Julie - I don't remember treating the boys in 2015).
Did some swapping around over the winter - moved the JR girls into that pasture in Feb of 2016(I think - have to go look at pics now). Then in March (AGAIN) found lice on several of the JR girls. EVERYONE treated in that pasture - think some of the boys showed up as having them too, couldn't find on my calendar. Boys have NO pine trees in their pasture, but have 3 other large ones + a persimmon outside of the paddock.
MARCH, 2017 - now. Bell is in the outer perimeter of the pasture with JR mares. The two May 2015 fillies - Chylly & Jynx - have lice . Chylly has them BAD. Her white areas were covered in little, moving red spots and she was looking poorly. THIS time treated her, Jynx & Blitzen with DE instead of the "nasty" stuff with chemical. By next day, they'd all "perked up" - ESPECIALLY Chylly, whom I'd started to worry about, actually.
SO - I will be doing more treating. Bell has looked a bit poorly, but other things going on, too. I haven't seen lice on her but didn't dig into her furry coat much, either. Maybe not enough to tell? She doesn't have the patches that the others have had... or that she had in the past (she rubber herself into many sores in 2015 on her neck, shoulders, rump).
So - is this on the property (with 30 equine now & working 11-12 hour days 4 days a week, it's difficult to get them all treated in the same 3 day weekend much less in the same day!) going to always have an issue with lice? Is it in the trees? Is it coming in from the hay? They seem to show up in March - even when we've been grooming/checking the ponies throughout the winter. AND this year so far, have to admit, I hadn't even done cursory groomings the way I was since work resumed in January...
I have to go to work, will renew this later...