I think it came from years ago when a minimal amout was effective. Six grown peafowl drink around 1 gallon per day. Apparently after arsenic quit being used as a wormer people turned to safeguard but after years of use it has become nearly ineffective in many parts of the US as some people did not worm properly and caused resistant strains. If you are in one of those parts you will have to use very large doses of safeguard; if you are not the minimal amount might still work. I remember seeing a map for goats and Safeguard effectiveness somewhere. As a side note I think there is still some mill out there that still uses arsenic it prevents blackhead as well. This is also where the old wives tale as to why you dont feed ducks and geese medicated chick starter came from. Ducks and geese are total pigs and they would eat past the lethal dose. Current medicated feed (amprollium) is nearly impossible to overdose on.