I admit, that cow was my first elk. And I was expecting the humped back I typically see when a solid hit is made on a good Mule deer. Often times the deer gathers itself up and runs up to 100 yds after the shot, but I had never seen a deer not react to bullet impact.
In many ways shooting a bull elk with a 165 gr bullet from an '06 can be compared to shooting a deer with a 60 gr 22 caliber bullet.
Either will do the job with proper bullet placement.
And I always remember sage advice given by several seasoned elk killers.
Keep shooting AIMED shots until all four of the elk's feet are pointed at the sky.