This horse Will. Not. Gain. Weight.
Back story: I've had a boarder (an ~10 year old OTTB, with kissing spine....basically retired) for the last four years. He came to me skinny and with bad feet.....he quickly gained weight (to the point of almost being fat!) and his feet improved to point where he is now barefoot and comfortable.
Last summer was a really hard summer on him. It was hot, and very buggy. He is OCD neurotic about bugs, and while my other two easy-keepers were happily grazing in the pasture, he would be trotting around the edges trying to escape the bugs. (He also refused to keep fly masks/sheets on for more than an hour at a time, and fly spray only works so well. Yet he flipped when brought inside during the day while his buddies were out.) He lost A LOT of weight, just from his constant self-exercising. Ribs very visible, etc. I know it's better for a horse to be skinner than fat, but he was TOO skinny, trust me.
Then over the winter (this would have been last winter) he gained back about half of the weight. To a point where he was still skinny, but not Call-the-aspca-skinny.
This summer, it was less hot and less buggy, but he still lost some weight, which put him approximately back to where he was the summer before. I would say that he needs maybe 150lbs, which is a lot on a lean 15 hand TB. And now I'm VERY concerned about him and how he's going to handle this winter. Especially because we spent the majority of this summer trying to get more weight on him and failing miserably.
His feed: He gets a huge amount of a quality Senior Feed, with soaked beet pulp and hay cubes and black oil sunflower seeds. Essentially all the hay that he can eat, and it's GOOD hay. Rich, well-fertilized pasture in the summer, 24/7. This horse has food in front of his face almost 24/7. And he eats it all! It's just not sticking!
His fecal came back fine. His teeth are fine. His feet are still fine. His coat is shiny. He doesn't have much of a top-line because he's not ridden, so that exaggerates how skinny he looks. We are going to start blanketing him (something which hasn't been needed the past winters because he was a little butterball) because I am concerned about conserving his energy.
What am I looking at at this point? Ulcers? He is a very vigorous cribber/wood chewer, which doesn't appear until they are regularly coming inside when it's cold. I know his owner can't afford a full ulcer treatment, but are there some cheaper gut supplements that would work?
Any other suggestions? Should I be looking into straight-alfalfa hay cubes, for example? What else puts weight on a horse? We had him on the Cool Calories 100 (a PURE FAT supplement) and it did nothing for him, even after going through the entire bucket.
I'm concerned not just for the horse but for my reputation. I know that's terrible to say. And his owner knows that I am taking the very best care of him and that it's not because I'm not feeding him that he's skinny. But even non-horse people look at my two fatties and go "But why is that other one so skinny?" My farrier comments on his weight every time he's out. It's noticeable. But I don't know what else to do!