A small OEGB hen probably weighs about 500 grams, so the minimum dose of .2 mg/ kg would be:
.5 x .2 / 18.7 = 0.005 ml, which is almost I'm possible to give.
That max dose I would give one that size is 1mg/kg which is:
.5 x 1 / 18.7 = 0.02 ml, which is about the size of a grain of rice.
This 1mg/kg is an amount that pigeon fanciers use.
the almost impossible amount, like end of a toothpick size?
Yes, so just give the larger amount.