A woman I board with vaccums both her horses and they love it. They look like they are about to fall asleep. The vaccum is an actual grooming vaccum though and it is VERY quite. Personally, I like good old fashion elbow grease :) but I do know what your talking about with that fine dust/sand. I like to use satin sheen and mane, tail and coat. Its fairly inexpensive and makes them very soft, and it makes that dust invisible until you are able to bathe them.
Works really well. Make a strap so you can hang the machine part over your shoulder as its movement accross the floor is more upsetting than anything else.
The problem I've found adapting the house vacuum cleaner is the brushes are at the wrong angle.
One place I worked at had the revolving brush type - absolutely awesome to use - you just had to be careful you didn't get too close to the mane with the end as it wouold tangle it and then pull it out.
A few years ago I tested a special vacuum cleaner. There were two special brushes with it, the same like for horse.
The brand was Super Dandy.
The noise was not very strong. That removed well the mud and the dust. My horse was very clean and happy because it massed him!
Now I think the technology evolved and we can find even more successful and less noisy vacuum cleaners.
I know that certain persons use the vacuum cleaner for the house, but I do not know if the result is similar or better.
I vacuum / blow dry mine from foals to adults using the large Electro-groom. I have never had a problem with any horse freaking out/pulling over the noise, sensation, or blowing air. With clippers and vacuums though I don't act like it is a big scary thing they have to get used to. I just expect them to mind their manners at all times and any horse stepping out of line is firmly corrected.
As for using a shop vac, I have used the 2-3 horse power smaller ones before I purchased the electro groom. You have to be careful which attachment you use because the animal vacuums have special notches on the nozzle to avoid pinching the skin. Look for a drapery-like attachment to help with that issue.
Edited to Add:
The results with the shop vacs are the same for dirt removal, but the animal vacuum seems to help more with actual coat shine overall "glow". As for noise, the shop vac is slightly louder.
With all the promising positive feedback, I have been eager to try it, but other projects around the homestead keep getting in the way. Perhaps after the holiday season I will have some time.
Thank you all for sharing your experiences.
A couple of places I have worked used vacuums, one halter horse trainer where every horse got vacuumed daily and a few different thoroughbred farms where the vacuum was part of the sales prep and sales grooming routine. The halter horse trainer we had the big electro grooms and for shows we had the smaller canister vac, the thoroughbred farms all used the big elecrto grooms. I MUCH preferred the big electro grooms, the performance difference I felt was huge. I really want to get one mostly for winter grooming but also daily grooming and have been contemplating talking to the barn owner where I board about the possibility of the barn getting one (because it's not in my budget for sure lol).