also, depending on their age - i give my adults oyster shells for calcium and grit.
you will have people tell you that you cannot use it as grit. i am here to yell you that you can (there is some dispute that it can cause damage to growing chicks that don't need all the calcium - that i don't...
i agree
while it may work, it may not be the best option. i am not an expert on what road salts and oils can do to a chicken. i live where we get snow 4 months out of the year, and they put salts on the road to clear them. that runs off onto the gravel, as well as the oils from tires...