As far as feed goes, In my opinion it should only be used as a supplement when one is out of natural forage, or your getting ready to eat them. How can one sell, honestly, range bulls out of a feed lot?
The concept of feeding bulls grain is a double edged sword. If he doesn't get enough nutrition he doesn't express his genetic merit. If he doesn't express his genetic potential, he won't be compared favorably to other bulls in his group or outside his group. The whole point is to identify the outliers, whether it be good or bad.
A shorter testing period (75-85 days) is, in my opinion, enough time for most bulls to show his potential without adversly effecting his longevity.
Bull tests used to be, in general, longer than they are now. Some were, and are still, 140 days in length, which is too long in my opinion.
The ration difference in these feeding regimens are a key factor in longevity also. Most Bull Tests feed a very high carbohydrate feed (lots of corn) so that the bulls will gain the most they can. This can be detriminal to overall bull health. IMHO
There is a big difference in "Testing" bulls and "Developing" bulls properly.
If you want to develop range bulls by implementing a "HIGH" fiber and lower carb diet and keep gain on a reasonable plane, the cream will still rise to the top and they will not be unhealthy.
Contrary to what some people think, I have never seen one "FORGET" how to graze when turned out with cows.
In the past, in my area, it has been more expensive to develop "Forage Only" bulls and the buyers will pay less for them.
Been there, done that.