How long after the last deworming was this fecal sample taken? If Quest dewormer was used last, you should wait twelve weeks before running a fecal egg exam. If other dewormers were used a shorter interval may be OK. It’s probably just easier to remember waiting twelve weeks after any deworming.
If the correct interval was used, there may be internal parasites in the intestine without eggs being present in the fecal sample. For that reason we recommend deworming all horses a minimum of twice a year, spring and fall. To follow this program, we also recommend fecal exams be performed spring and fall at least twelve weeks after the last deworming. These fecal exams will insure the horse is not harboring more worms because of increased exposure or decreased resistance to worms.