I use Eprinex pour on (product 67641) for beef and dairy cattle to be put on back of neck of chicken under the feathers on bare skin. It gets worms, mites, lice and all others we usually worm for and treat for as external parasites.
Best is you can eat the eggs the next day.
Or, on all other types of animals, drink the milk, eat the meat, the next day after using this. Also good on other farm creatures like on your dog for worms, ticks or fleas. Put on skin where neck hits back.
I use 1/2 ml on a regular size chicken, double the amount needed but the amount of overage is very forgiving but I know, "wasteful". Use a 3 ml syringe minus needle and that will do 6 chickens or as recommended by maker, 12 chickens at 1/4 ml per. Cost $41.00 for enough to do about 500 treatments. Recommended once or twice a year by maker.
Fill free to call them and speak to to an advisor as directions on container are for large amounts of chickens.