I just discovered a tumor on his chest. It's very hard and larger than a softball. His fur is such that it was very difficult to see and he's a bit squirrelly and doesn't like you to touch him. Any idea what this might be? I have a horse vet coming out to my house on Friday but he has to be confined when the vet gets here. That is going to be a challenge because he hates having a collar on and goes crazy if you try and confine him. He's a free spirit. His brother is much more open to a hug. He is about 8 years old. Any advice would be greatly appreciated.