Hunterofelk....
That's rough luck man! There's so many things that could have caused this and without looking at it closely its hard to nail down the culprit, but considering you didn't get too many replies I thought I might give ya a few ideas of what could have caused it, or the usual most common issues.
The worst things for a mount is sunlight, smoke, and moisture, so if exposed to any of these it could have worsened the issue. If the wall, such as Timberstalker suggested, had stain the oils/chemicals could have degraded the hair, causing it to fall out.
The other issue, that most people sometimes find, most of the time too late, is mites. Carpet beetles, mites, flesh eating beetles can get into mounts and start to eat the roots of the hair and leather which causes hair to fall off. These bugs LOVE this type of thing and usually you will start to see damage near the peticles of the horn/antler and the hair line and in the back, where its more dark. I would check around the rest of the mount and if you find spots where there is missing hair I would guess mites; sometimes you can detect small remenants of shed shells from the mites at the affected site, but they are VERY hard to see or detect. The only way to stop this is bug bomb your trophy room regularly. If its only on the back of the mount as pictured then its most likely the stain that seeped into the hair causing it to fall out...it also looks like there was some moisture there at one time due to the hair still sticking to the wall.
The last potential problem, which I am hesitant to even suggest for reasons of that I don't want this to turn into an argument on methods of tanning..but it could have been a poor tanning method/job...but again, I would think you would have issues elsewhere on the mount if this were the case.
Hope this helps and sorry about the mount, Joel/BRT
