Just the same sorta 'common sense' thing I'd thought, before diggin' to the bottom of it (puns intended). I've revisited the use of diatomaceous earth as an anthelmintic, and it turns out your statement, indeed, appears to be correct (which makes me incorrect ~'-)
Here's the typical comment found online:
Although there seems to be anecdotal evidence for efficacy, not controlled clinical studies have proven these compounds to be effective.
And, here's a snippet from *controlled* clinical study:
CTRL and DE steers had higher parasite levels than CONV steers during the 1st (P < 0.01) and 2nd months (P < 0.05) after treatment. Egg counts for CTRL and DE groups decreased in March and none of the groups differed (P > 0.05) significantly for the remainder of the study. Coccidia levels decreased over time similarly for all groups. Offering 20 g DE per kg food intake for 46 days to beef steers on a high cereal-based diet had no effect (P > 0.05) on body weight, average daily gain, dry-matter intake, food conversion or days on food compared with the untreated control steers.
From the clinical study entitled: Effect of diatomaceous earth as an anthelmintic treatment on internal parasites and feedlot performance of beef steers
Fernandez, M.I., Woodward, B.W., Stromberg, B.E.
Dept. of Veterinary PathoBiology,
College of Veterinary Medicine, University of Minnesota,
St Paul, MN 55108, United States
SoOo ... reckon I'll have a cup of that coffee that the studies can't seem to agree upon either (not that bein' proven bad for me would slow my consumption much ~'-)
