You may want to check out fact sheet #23.

I think a wise suggestion is to not use it as a sole forage source, especially if you are under drought conditions.

The other thing is:  I believe sorghum-sudan will regrow faster if you don't cut/graze it too close.  Allow 6" stubble for faster regrowth. This may not be as important in grazing. However, we have found this to be a critical factor when harvesting as silage.