I used to have a horse that was heavey, and I fed Spirulina powder in her feed. Worked really well with her, and I also know of another person that had a horse with much worse heaves than mine, that it worked really well on also. It is pretty cheap, you can buy it by the pound from herb suppliers on the net. It is pretty powdery, so it has to be mixed in with something tasty, I used a grain mix with some molasses in it to disguise it. I got the idea from the Horse Journal, they had an article on it some time ago.
My horse is on MSM already for his joints (~10,000mg in his supplement) but when he had a really bad allergy/COPD/RAO episode a couple of summers ago, my vet had me double dose his MSM. I just bought plain MSM and gave it on top of the joint supp so he was getting about 20,000mg/day. I think some people actually do a higher dose than that for short periods of time. I can't say for sure that it did or didn't help (we had to resort to a couple of doses of steroids to calm his immune system down) but now if his breathing starts to get noisy, I immediately increase his MSM and his Histall. So far *knock on wood* we haven't had any more bad spells like that. His seems to be triggered by allergies and we've made a few other changes to help support his immune system too so things don't get out of hand.
"Farming looks mighty easy when your plow is a pencil, and you're a thousand miles from the corn field." --Dwight D Eisenhower
My horse has COPD. He has never come bad enough to use it, I only soak his hay which keeps him happy. However, when my vet saw him she suggested MSM and siad she saw great results. It is worth a try seeing as it is quite inexpensive. However, if your horse doens't even have too bad of a case (as mine doesn't) you may not notice a difference.
I have two with COPD. One is far worse than the other. I have found that the MSM makes a HUGE difference in their breathing. Also on days that they seem particularly bad, I use a product by Finish Line called Air Power. I read about it here on COTH and decided to try it. It's truly amazing. My one boy that has the less severe case is still in work and when he gets bad, I just give it to him twice a day and you really wouldn't even know he has COPD.
"Be the change you want to see in the world."
I know this is an old post but wanted to add that I took a 22 year old QH mare, because the old owner said she had heaves and was no good anymore. Over the summer months she was having a hard time and I even ended up having to giver her some antihistamine/steroid shots which could have ended up being pretty expensive if we needed to do it on a regular basis so I did some research and came across an article on MSM helping with respiratory diseases. I started her on it last fall and we've made it through this summer with no difficulties like the previous year. It's an inexpensive miracle for my old girl. Now that I feel like her breathing is under control we are able to go out on rides with her 15 year old human girl and her 13 year old Morgan boyfriend.