A fecal exam checks a fecal (manure) sample for parasite (worm) eggs.
A fresh manure sample is mixed with a special solution that concentrates and floats parasite eggs present in the sample. The eggs adhere to a cover slip that is placed on a glass slide, which is then examined under a microscope. Any eggs present are counted.
The eggs of strongyles are most commonly found in adult horses, while ascarids are more commonly found in young horses.
Tape worm eggs, which pass out of the horse in the tape segments, are hard to find. There is a blood test available that better determines tapeworm infestation.
Ideally, there should be no eggs present. If the sample was taken 14 days after your horse was dewormed, it indicates that the parasites have built up a resistance to the dewormer that was used.
A yearly fecal exam is recommended for all horses. It is best done in the spring, when internal parasites are gearing up to contaminate your pasture with the most eggs.