I read a first hand account of a man that helped gather a herd of Tule elk in California in the 1920's. Many of them were roped and tied down for transport. Unfortunately none of them survived the trip. I would say it's quite possible that a horse could hold an elk however it may not do the elk any favors.
There's nothing like the Rockies in the springtime... Nothing like the freedom in the air... And there ain't nothing better than draggin calves to the fire and there's nothing like the smell of burning hair. -Brenn Hill