I also read to place it on the neck...so the 2 drops on the vent would actually be ineffective, since the dosage is not even close. I hate to correct people but want the birds to get proper treatment.
I'm never too old to learn but someone said they put drops of Ivermectin under the chicken's vent to worm them. I can see if you were treating for lice but if the worms are inside, I consider that impossible. However I read you can put the Ivermectin on their neck to control worms, so maybe it...