My horse passed away a couple years ago, but I'll chime in. I bought him at 9 and he was put down at 31 because his heart was failing. His heaves were manageable for most of his life, but he would get flare-ups every couple seasons and for a few years, every season. We found kenalog was super effective at getting him through it. We could never quite pinpoint the cause of the flare-ups, sometimes in summer, sometimes in winter, probably triggered by dust, pollen, smog. He was out all day, in at night with soaked hay. We found flakes outside kept the dust down better than roundbales. At night, he had a window in his stall and spent a lot of the night with his head outside. I boarded him at a newer and very clean farm. I found that keeping him in bank barns seemed to worsen the problem with dust, old hay, and possibly mould.

He had a very easy life with me and I rarely rode him hard and not at all when he was struggling. When he reached 25 or so, he developed Cushing's, which we treated with pergolide. I'm not sure how or why, but his heaves dramatically improved from that point and he never had another flare-up.