I mix my supplements with timothy cubes, some grain, carrots and water. Both my horses eat them that way just fine. I am also at a boarding farm, but make it a point to be there everyday to feed this to them because I feel it is my responsibility to do so. For those who cannot be there, the farm will make it, but there is, naturally, a fee. I also leave packages (a week’s supply) for each of them, just in case weather intervenes and I cannot get there. Perhaps your farm could do the same? We have several horses who need supplements, not just mine, so it isn’t that they only have to do this for one or two. Smartpak will even deliver your supplements to the barn where your horse lives, if asked.
It is never the horse's fault