My old horse started coughing a few days ago when I was riding him, he was fine in walk then when I asked him to trot he coughed a few times, then again when I later asked him to canter. The next day he was simialr although worse Today I just took him for a walk to see how he was and he coughed a few times just when walking, and quite badly, almost like he had something stuck in his throat. I am quite worried about him. He doesn't seem to do it at any other time, only when ridden, he doesn't cough in the field or stable. And it has come on very suddenly so I don't think it is dust related as nothing in his environment has changed. I wonder if maybe he got too cold one night and has caught a cold? He seems fine in every other way, though I did mean to take his temperature today but forgot the thermometer! His nose is a bit gunky after he's coughed. Has anyone any ideas what could be wrong? Can horses get coughs like humans do and is there anything I can give him to soothe it/make it better? I tried calling the vets but only get the emergency line now as it's the weekend and don't know that this counts as an emergency. I don't know what to do, any advice greatly appreciated.