A few weeks ago we moved my horse back to our old barn after boarding at a different barn for about 6 months. Not long afterwards (a few weeks maybe) I had him on cross ties and noticed that he was not passing very much poo at all, but what was there looked quite normal. He is a 15 y/o grey Connemara gelding and has had melanomas under his tail for a while now, but up until this point they had never actually caused any problems. This made me look at the rest of him to see if there was anything else wrong and then noticed that he was also breathing too quickly and heavily. I was concerned that he had some kind of digestive problem and walked him around until a vet showed up, and they said that his lungs sounded normal and his gut sounded fine but a bit inconsistent and gave him a rectal exam, which was mostly normal other than his rectum was slightly smaller than it should be due to the melanomas. They decided that he was probably breathing hard because he was dehydrated and stuck a hose up his nose and pumped in a concoction of water, mineral oil, and a bunch of other things, but also gave us some antibiotics in case he had an infection.
Now it's a week later, and the infection that they said should have gone away in a few days hasn't changed at all. We don't think it's an infection anymore, although he is still having as much trouble with the heavy/too quick breathing and passing his poo. Another vet has said we need to take him to the area's horse hospital to get an evaluation about possible treatments for his melanoma problems which are only going to get worse as he ages.
Ok, so sorry that was so long and I appreciate anyone who read it all. My main question is whether anyone has had any experience with something like this or knowns about anything similar. I am suspicious about just blaming it all on the melanomas, since the pooping problem came on suddenly (which doesn't entirely make sense if they were growing slowly) and it showed up at the same time as the breathing issues right after we moved to a different barn.
Thanks for your help or at least taking the time to read this.