There's never been any CONCLUSIVE evidence that shows any benefit to FEEDING DE to anything.
Um, according to the source I listed, the "benefits" were reduced parasite loads for Capillaria FEC, Eimeria, and Heterakis, as well as better weight gain, greater numbers of eggs laid, larger eggs, more albumen and yolk in the eggs, and reduced numbers of northern fowl mites. As far as this particular study is concerned, there is, indeed, "conclusive" evidence -- as per their
conclusions.
if you read it carefully you'll see it wasn't all that scientific, and only showed a slight improvement in one breed of birds.
Um, again, I'm not sure what constitutes "scientific" for you, but a university-led study conducted by the avian sciences department is scientific enough for me. The study included fecal egg counts and postmortem examination, both of which provided science-based, as opposed to anecdotal, conclusions. Maybe you were just being particular about the kind of "science" you expect, but when the article was published in Poultry Sciences it kind of lent more credibility to the study as a one based on scientific fact. It is also misleading to suggest that the test only showed benefits to one breed -- they only used two breeds in the study. More tests on many more breeds is definitely in order. What I will agree with is the fact that just about every retailer and "natural/alternative" website that I saw used that one and only study as the basis for its claims. Also, I noted in my original post that few if any other studies seem to exist to prove or disprove the results of this particular study. Which brings me to your last statement:
The main reason you don't see a LOT of studies is most scientists already know an inert substance has little effect on internal parasites
Are you kidding me? That's like saying, The reason surgeons didn't wash their hands was because most scientists didn't think there was any such things as "germs". (We can all thank Louis Pasteur for his theories and subsequent discoveries, but just because no one else had proven it didn't mean it wasn't true.) Thus, while other scientists may not have attempted to reproduce the results of this particular study, either on the same breeds of chicken or other breeds, doesn't necessarily disprove the results of the first test. That is one reason I asked if anyone knew of any other studies.
For what it's worth, I think DE is overrated. I've used it in the garden and on my birds without any obvious benefit. I'll take a research-backed pharmaceutical or "chemical" any day over DE. I just don't think it's helpful to claim that it's worthless if there is even some evidence to suggest it may have benefits - whether they're external or internal. My original question was whether or not it produced more harm than good. You can't negate the study that exists just because you personally disagree with the results. Show me a published, peer-reviewed study that shows DE is ineffective as an internal supplement or external remedy in any or all breeds of chicken and I'll be happy to stand behind your words.
