Sorry about your hen. How does her beak smell? Have you had any fowl pox in your flock? As others have said, these kinds of lesions inside the beak can be from the wet form of fowl pox, canker (a protozoan infection,) but unfortunately can be a malignancy. The white color kind of look like that unfortunately. But it is a good sign that she is eating a little better. I would follow @casportpony ‘s advice on asking the vet about the Baytril for a bacteria or the metronidazole for possible canker. She has more experience than I do with these things. Unfortunately if it is indeed cancer or malignancy, it will become apparent soon.
