Yeah but horses weigh a lot more than humans. I haven’t seen these syringes but I can envision what you are saying. I know the dose is calculated in mg/kg, and I suppose a newborn foal might use less than her mare, closer to that of a full grown human, thus the notches. Those notches probably help a lot with measuring. The thing is, different protocols for prevention vs treatment. Maybe not dramatically different.
You don’t worm foals.