It looks like bumblefoot. I have the Chicken Health Handbook by Gail Damerow and it looks exactly like the picture on page 254. The book explains that this is a fairly common and is caused by a staphylococcosis infection that enters the foot though a cut. This bacteria is present wherever ere are chickens so you can't really prevent the bacteria, just avoid the infection by avoiding the injury. The injury/cut can be caused by a splinter gotten on the roost, jumping from the roost to a hard or rocky surface, housing on wire, irritation due to improper littler management. It also says it's hard to cure and suggestions injecting the swollen area with 1/2 cc penicillin/streptoycin. If the abscess is large, wash the foot, cut open the abscess, squeeze out the cheesy core, rinse well with hydrorgen peroxide, pack with Neosporin, wrap with a bandage or strip of clean cloth and tape. Then, confine the bird on deep litter and redo the dressing every 2-3 days.
It suggests some ideas to prevent it such as not having high perches, sanding perches, having good sanitation, deep litter, etc.
Hope this helps. Don't know about the other issues this chicken is having that you mentioned. Great resource, Damerow's book, it might help you diagnose those other issues. I use it all the time for chicken health related things. Bought mine used on
Amazon.
Guppy
