get sheep wormer and give them 1 mil lot more afective.
Withdrawal period?
Good point Rosemary, however it won't be the same in a different species therefore even what is written in the leaflet for sheep won't count for chickens.
In fact, I wouldn't give anything to the chickens that is supposed to be administered to another species. And
only if it was an emergency, I'd try my best to work out the correct dose, not just a random "1ml of something". The administration route can also vary the effect. Something that is supposed to be taken orally by a sheep, which is a ruminant, will not have the same effect on monogastric like hens. Sheep/cattle strength medicines can harm smaller animals and birds have a much faster and somewhat different metabolism from mammals.
Veterinary drugs destined to a specific species have been studied and tested, the differences are there for their benefit, and not because somebody thought fun to make many types.