You can apply either, I use spray vegetable oil, vaseline is also good, it is a personal choice as both work well making sure that the legs and feet are well saturated with the oil and leave the chick alone to do its own thing. Repeat daily for two weeks.
5 grams of Amprolium to 4 liters of water continuously for 5 to 7 days. reduce to 3 grams per 4 liters for another 5 to 7 days. This gradual reduction in the level of treatment assists the birds to developed immunity while maintaining some level of protection. Fresh solutions should be made up...
Looks like leg mites, treat with petroleum jelly or vegetable oil every day making sure to soak the legs and feet well for two weeks. It takes time for new scales to grow but the mitres will suffocate at the first treatment.
Sound like it is coccidiosis need to be treated with Amprolium as it is called in Australia. Google coccidiosis and see what the treatment is called in your part of the world.
Isa Browns tend to have reproductive problems once they reach roughly the age of two. This is because they never have a rest from laying as the heritage breeds do during winter. They are little egg-laying machines designed to do nothing but lay eggs. The average life span of these chickens is...
I have a girl with the same problem, so I had her implanted by the vet to stop her from laying altogether, it lasted for 5 and 1/2 months. She had no problem after that but on vet advice I only let her lay for 6 months at a time and have her implanted for the other part of the year.
I use a tube of fluoride toothpaste with a slot cut into it and place it somewhere the girls cannot access it. In a few days, the rats will eat it and die. It saves on having poison around and does the job.