I have such a small flock, I am not too worried. I just don't think that stuff...runs...off? They..may, get some on the ground when they do the dirt bath, but this is really a very small spritz here and there.
The problem is over application and runoff. If you are careful it should be ok. A lot of home owners use way too much--they do not follow the instructions.
It is only supposed to be used every two weeks too.