I will just say that
DE does work for killing internal worms. I know because I have used it for quite some time now. My birds eat earthworms, flies, and whatever else kind of bug that happens to cross their path, and pick around in the dirt and
they have been worm free for as long as I've used DE in their food, just over a year now. That's proof by using it, not by reading something. I don't have money to throw away so
I certainly wouldn't be using it if it didn't work.
And that's not anecdotal evidence, it's real evidence. I didn't do a little 2 week study on lab birds, It has worked for over a year now on my free range chickens and turkeys. I don't know if it kills or prevents any other kind of parasite, but worms? YEP sure does.
Have you done fecal egg counts to determine if they
have parasites, or are you just going by a lack of symptoms?
Do you know for certain they had worms BEFORE you started feeding them DE?
My birds free range and eat all the same things yours do and I've
never had any signs of a worm infestation.
But I haven' given them ANYTHING at all for worms, so ANECDOTALLY, I can tell you doing NOTHING works as well as feeding DE
Unless you've done
testing for parasites and used a
control group, yours IS "anecdotal" evidence. Length of time doesn't change the definition:
http://en.wikipedia.org/wiki/Anecdotal_evidence
The expression anecdotal evidence has two distinct meanings.
(1) Evidence in the form of an anecdote or hearsay is called anecdotal if there is doubt about its veracity; the evidence itself is considered untrustworthy.
(2) Evidence, which may itself be true and verifiable, used to deduce a conclusion which does not follow from it, usually by generalizing from an insufficient amount of evidence
In science, anecdotal evidence has been defined as:
"information that is not based on facts or careful study"[2][verification needed]
"non-scientific observations or studies, which do not provide proof but may assist research efforts"[3]
"reports or observations of usually unscientific observers"[4]
"casual observations or indications rather than rigorous or scientific analysis"[5]
"information passed along by word-of-mouth but not documented scientifically"