No need to waste money on a fecal sample. Just pull down their eye lids and see how white to yellowish they are. The more yellowish, the higher the worm load in their guts. You need to treat anyway, so go ahead and deworm them. DE does not work when it reaches this stage, so treat with Ivermectin as recommended. It is not overly cheap, but works well, especially if you have not used it a lot. If you have, treat with a different type of dewormer to stop parasite resistance.
Even by organic standards, when the worm load reaches this level, ethics kicks in and organic rules require treatment of the animals.
Common Weeds And Wild Edibles Of The World (HD video)