Large scabby growth on chicken belly

[ozarkchickens]

I have a lavender Orpington with a large scabby growth on her belly, centered near the base of her breastbone well below the crop but forward of her legs. It's almost like a goat's horn in texture and hardness; when I picked her up and felt the lump I assumed it was rock hard dried poop and took her inside to clean her up or cut it out. Not. The pink skin is growing up around the edges of the lump. Her appetite, poop, behavior are all normal. She is 2 years old. She eats organic layer, free choice calcium, a little protein/calcium each week (scrambled eggs, cottage cheese etc) and greens daily. I picked her up because I thought she had a slight limp, but no signs of any issues. Any thoughts appreciated, no poultry vet here...

 

[DocBirdBrain]

Your description of it feeling hard, like a goat's horn, makes me wonder if it is a keratinized mass- a growth (tumor) of the skin involving keratin, the stuff that makes feathers, nails, and horns. Hyperkeratosis (exuberant growth of keratin not associated with a tumor) can also occur as a result of chronic skin irritation or at an area of a previous injury, but your photo looks a bit extreme for that.
There are several different types of keratinized masses, some are benign, others are malignant. If that's what it is, it's not painful and I don't know of any treatment (short of removing the mass under anesthesia and submitting it to a pathologist for a definitive diagnosis). As long as she is eating well and behaving normally, I would continue to monitor it.

Here's an overly science-y article on skin diseases in birds (written by a pathologist, it may not be any help to you at all, sorry about that):
http://www.tandfonline.com/doi/pdf/10.1080/03079458908418580