I don't and they have all been pretty healthy. Some people do, that is their decision. Mine get started on chick starter (non medicated) and they eat like there is no tomorrow. I figure if they get sick, I don't want them in my flock anyway. Only the strong survive. Some people may have a problem with this, but I like knowing that my flock is strong.
I use the small chick waterer and I put 5 drops of Poly-Visol (enfamil baby vitamins without iron) in the water everytime I change it until the chicks are about 4 weeks old.
I have not lost a single chick. Don't know if I can attribute it to the vitamins, but it surely can't hurt.