Sorry I haven't been able to get back online to update... this had been a nutty few days, between the heat and assorted small crises, horsey and otherwise...
Scout colicked last Tuesday afternoon. He'd been outside all morning, brought him down for his afternoon feeding at 4 pm. He was acting dopey and out of it (best way I can describe it...), breathing a little heavily (not really distressed per se, more like coming off a workout), and not at all interested in his grain or hay, and laid right down in his stall. Being a little dozey and laying down in the afternoon isn't too unusual for him, but ignoring food is a major red flag for Mr. Bottomless Pit, and with the recent respiratory issues his breathing is obviously something I continue to monitor and track. I stood and watched him for a few minutes, mainly to see if his breathing would relax on its own (he could well have been cantering circles right before I brought him in, for all I knew), or if he was having an attack. Within fifteen minutes, he was on to an absolutely textbook case of colic. Nosing at his sides, wanting to not only lay down but also roll, a couple of little poos, but very little and far greener and looser than is normal. I'm attributing his slightly elevated breathing that afternoon to the colic and not to heaves at this point.
Some walking and some bute and banamine later, he was fine; came right out of the colic and did fine overnight, was his old perky self by the next morning; eating, drinking, normal poo, good gut sounds through the stethoscope.
So, after that crisis came figuring out the reason for the colic. I know exactly what he ate and had access to in the barn; nothing amiss in his hay (I'm already checking that for anything even slightly out of place before I soak it) or his grain, no changes in his grain, supplements, etc. With that in mind, I concluded that whatever upset his system, he found in the pasture that day. I headed out and took a sample of anything that wasn't grass and started identifying. As dry as it has been, the good grass is really starting to die back, and I wouldn't doubt that the horses may be looking harder at things that they wouldn't otherwise.
After some research, I discovered that there is a significant amount of ragweed out there. NOT ragWORT, which I know is quite toxic to horses, but ragWEED. A) not good news for his respiratory issues. While we aren't quite to the time of year when the stuff starts flowering and pollinating, I'm not waiting until that time comes to do something about it. B) it just isn't "horse food," whether it is what actually caused last week's colic or not. C) for all I know, just eating the stuff could be triggering his heaves attacks -- I haven't found any sources saying that allergies could be triggered by eating ragweed, but I haven't found any sources evidencing the contrary, either. At any rate, I've been pulling up all the ragweed in the pasture (and everywhere else I see it around the farm) for the last few days. None of the other weeds that I sampled were anything to worry about, or out there in any real quantity (i.e., 3-4 small individual plants spread over a half-acre paddock).
Scout has been in the barn since his colic; I don't want to risk him getting into the ragweed that hasn't been pulled yet and colicking again, and it has been too bloody hot for him to be out there without shade anyway. The weeding process has been slower than I'd like due to the heat as well, but it's getting done as quickly as possible, with care to remove the roots and dispose of the plants away from the barn and pasture. I've been hand-grazing both of the horses during cooler hours, keeping an eye peeled for any ragweed in the area. We did get a little rain two days ago, and again last night -- not enough to put water back in our creek, but the pasture grass is greening up a little, so perhaps weeds won't look so much like a dining option now.
On the bright side, Scout has had absolutley ZERO observed coughs since his colic last Tuesday. I'm really beginning to think that exposure to the ragweed has been our problem all along -- both of his heaves attacks as well as his colic episode occurred during/immediately after being out in the pasture for several hours, and this entire saga began soon after he started going outside regularly for hours at a time back when the winter weather broke in late April/early May. He hasn't breathed or apparently felt as good recently as he has since he's been stuck inside due to the heat and the ragweed discovery. So, now I'm continuing to watch him like a hawk, keeping up with the Tri-Hist supplement, soaking his hay, and other heaves-maintenance/control measures, and keeping my fingers crossed that this is just a bad ragweed allergy and a heinous year for ragweed. It's definitely been a learning experience for me; I don't have seasonal allergies myself, and never knew what exactly ragweed looks like until now. I know I'll never mistake it for anything else after all this...
Anyway, that's where we're standing now.
@Barry: I have been taking note of everything so far, every little hiccup or out-of-the-ordinary thing, and the conditions at the time of the observation. He has been observed by the vet when the asthma-like attacks were in progress, and she has also heard his coughing in-person. I keep records of the type and quantity of his grain, hay, pasture, and water consumption as well as his weight in general, and have those records going back to his purchase in May 2009. I will look into video-taping his coughing at the next opportunity, although the coughs are so rare, sudden, and brief that I doubt the camera would turn on before it was too late to capture on film. I've been taking all possible precautions regarding his bedding, hay, and housekeeping to prevent another "asthma attack." I also have a vial of dexamethazone on hand in the event of another full-blown attack, and he is on a twice-daily regimen of antihistamine supplement as per the vet's instructions. I'll look into sugar beet as well -- I've never seen it at any of our local feed stores before, as it isn't a high-demand item in the area, but I will inquire. Thank you so much for your suggestions and comments; Scout and I both greatly appreciate it!
@Saddlebag: I'll look into getting some specific wheat-straw; I've never seen an ad for straw differentiating between wheat and oat before -- If I can get my hands on some definite wheat-straw, I'll give that a try.
Mesh hay nets make me a bit nervous; Sister's horse once managed to get his teeth caught in one (hung at proper height and everything), resulting in a slightly traumatic experience for him. I do have a canvas hay bag around. I've also heard and read that feeding from the ground was preferable as it reduces any dust falling into the airway? I already do spread the hay around the pasture in the winter, similar to what you describe, mainly to simulate more natural grazing activity, rather than standing next to a pile until it's gone. I will definitely see what I can do to slow his feeding down and avoid that excess diaphragm pressure. Thank you again for all of your suggestions!!
Anyway, there's the novel of the day... Cookies to all who read this... It may take me a while, but I'll continue to post updates and news as I can. Thank you again to everyone!!