Per the roster at Colts.com Rushing and Herald are on IR.
I also don't see RB Clifton Dawson and LB Marcus Richardson on the roster.
I haven't figured out who the 5th cut is yet.
Keiwann Ratliff seems to have secured his spot on the roster as the 5th CB. Perhpas they keep five or six safeties and five corners. If so, I'd live to see Silva remain. He's impressed me on special teams.
(Edit): P/K Adam Crossett is no longer on the Colts.com roster