First, DE is not an herb so does it even count as an "herbal" anything? It is however "organic" (used with no additives) as it's nothing more than powdered stone.
The subject (DE) has become almost as "deadly" to a discussion as religion, politics, or gun control... but for the record, and IMHO, based on what I can find/determine... I think, if you really dig, the DE (food grade ONLY) is used in the feed primarily as an anti-caking agent (absorbs moisture/abrasiveness keeps the feed from sticking?) & not to reduce/eliminate/control parasites in the intended consumer of the feed. Secondarily it is used to control the insect population/load in the feed and the associated contamination of the feed by the waste produced by same. It is used for these purposes to NOT pollute/contaminate the feed (intended for internal consumption) as typical pesticides would (harming the intended consumers). By doing these things, it may provide
some of the benefits stated on your link, (which just as an aside, is a website created by the producer of the product they are promoting). Could it be that the prevention of insect/waste contamination of the feed and NOT using commercial pesticides to achieve this, may have led to those benefits rather than direct ingestion of the DE?
MANY sites are quick to document that the FDA has determined that (food grade) DE is "safe" when ingested and/or used properly, or that it has been deemed "non-harmful" if ingested or handled/used appropriately. But, that is NOT the same as stating that it is effective and suggested for use against internal parasites. (Many of these same sites also recommend/strongly suggest the use of a breathing mask while in the presence of DE powder to prevent inhalation)
There is loads of documentation on the uses of DE in a DRY environment to control insects with exoskeletons, their larva and eggs; fleas, flys, bed bugs, roaches, ants, even scorpions and the like because of
how it works. (many pest applications using DE as the primary descant ALSO add pyrethrins <from pyrethum flowers natural, or synthetic> to the DE to act as a quick kill mechanism - read labels carefully) When discussed for use against internal parasites however, there are arguments in both courts, and very little actual scientific documentation to prove either as definitive. I have found links to tests proving how effective it was against worms in animals and other tests proving it was useless. There are lots of non-scientific (observations) reports about improvements in all sorts of animals (including humans) when fed DE.
However, since the primary method of it's success is the ability to dry out the intended victim (desiccation), it's use in a wet environment (internal/gut) would eliminate it's primary method of operation. The use of DE for insects is repeatedly stated as inadequate/useless in wet environments. It doesn't work when wet.
http://npic.orst.edu/factsheets/degen.html http://cals.arizona.edu/urbanipm/pest_press/2006/september.pdf http://equusmagazine.com/article/diatomaceous-earth-dewormer-15880
I think that if you want to use it and believe that it works in your situation, by all means do so, just back it up with fecal evaluations of effectiveness. Document before and after to show it is actually decreasing/eliminating existing parasite loads rather than just helping prevent those loads in the first place. Because if you don't have a worm load to decrease, it may or may not be the DE that's keeping the parasite bloom from occurring in the first place. So many other factors are involved. As a preventative, how can you honestly/categorically state it's the DE that's preventing the/any increase?
I guess you could do multiple tests over time with/without DE and see if there's any document-able evidence either way... But then who wants to intentionally give their animals/allow them to develop a heavy worm load?
