The vet came out today and scoped Cash to see if he could determine the cause of the nosebleeds. The good news is that Cash does NOT have gutteral pouch mycosis - which is fantastic news, since the fungus can be fatal. However, he MIGHT have an ethmoid hematoma - the vet saw a small area that could be the beginnings of one, but he's not entirely certain. It could also just be the super dry air and the dust causing the problem.
The plan is to keep an eye on the nosebleeds. If they increase in frequency or severity we'll scope him again and see if there's been any development, then form a plan of action from there. Otherwise, we'll just keep our fingers crossed that this was a one-time deal.
I also checked with the vet about possible photosensitivity to alfalfa, since Cash has been super itchy of late. However, he thinks it's just a slight sunburn and recommended a full-length fly mask and possibly a fly sheet as well (challenging because of the heat). Ideally Cash would be kept in during the day, but he goes a little nuts when he gets put in the stall and the other horses leave the barn, so that's not an option. I suppose I could leave Cash and Saga or Taran in the barn area during the day, but there's no guarantee they'll stay in the shade. Ah, the joys of owning a white horse!
Also, many, MANY thanks to MC who met the vet when I couldn't because of my work schedule. It is incredible to have friends who are willing (and able!) to do something like that, and I am very lucky to have such a friend. Thanks MC!