Horseman's Lab actually does a fecal egg count, thus the result that is given in eggs/gm.
However, you've pulled it at the wrong time of year and too close to the last deworming to really give you a good idea of what kind of egg shedding your horse normally does. You need to run a fecal egg count after your spring deworming (3 months later if you use ivermectin and 4 months later if you use moxidectin) and use that result to base your deworming program around. If the fecal egg count at that time is still 200 or lower then you would go with minimal deworming. But with it being 100 in the WINTER less than 2 full months after you used ivermectin and at his age, he is likely to not have much of a resistance to the parasites and therefore in need of deworming 3-4 times a year. When he's older then you may be able to get away from deworming as often because he's still in that stage where he is going to be developing his resistance.
Winter is the time when you have your lowest reinfection rates because the temperatures aren't conducive to strongyle larva maturing into the infective stage in the pastures/paddocks and also because horses tend to be eating hay rather than grazing and living in stalls where feces are removed daily. The summer months are when you have your high reinfection rates because environmental conditions are right for strongyle larva to mature to the infective stage and to remain viable on pastures.
Contrary to the old idea that all horses in a pasture should be on the same deworming program, it's now known that 50% of adult horses will control parasite infections on their own with minimal deworming (twice a year). So, it's best to test all horses to see what kind of parasite egg shedding they do and then put them on an appropriate deworming program based upon how many eggs they shed. They don't all need to be dewormed at the same time unless they all have the same resistance to parasites.
Licensed Veterinary Technician