I have yet seen one study that says that DE controls internal parasites. What I have seen is a very good sales pitch that does not have the science to back it.
Here is a quote from Dr. Christine King
Diatomaceous earth
"One of the most commonly used ingredients in these natural dewormers is diatomaceous earth or
diatomite. Diatomaceous earth is a naturally occurring, soft, chalky rock that, when crushed,
yields a fine, light-grey powder. It consists of fossilized remains of tiny hard-shelled algae called
diatoms. Owing to their high content of crystalline silica, diatomite is mildly abrasive.
In fact, that is the mechanism by which diatomite is purported to kill intestinal parasites. It is
believed that the abrasive micro-surfaces of the diatomite cut the outer membranes of the
parasites like thousands of tiny blades. But I question that premise. Industrial-grade diatomite
has a high silica content and is used as a mild abrasive. However, food-grade diatomite has a
much lower content of crystalline silica, so it is minimally abrasive.
And even if the abrasion theory is valid, then what does this stuff do to the delicate lining of
the digestive tract? While I could not find even one scientific study which validates the use of
diatomite against internal parasites in horses or other livestock, my search did turn up several
articles documenting the health risks of chronic exposure to diatomite. When inhaled, it causes
inflammation of the airways and, with chronic exposure, even some fibrosis (scarring).
Even more concerning was a study which showed that chronic oral intake of diatomite can
damage the intestinal lining, altering its absorptive properties and making it more permeable to
potentially harmful substances. So, it seems to me that the practice of using diatomaceous earth
as a daily dewormer for horses is either useless but harmless or useful but harmful, depending on
the grade of diatomite used.''
Chris