Daviyon Nixon, a big-boy DT, is on campus and is expected to man one of those D-tackle slots next year after he makes the academic transition from Iowa Western CC. But a big part of the D being gassed late, despite the rotation, is on the offense. With that 17-14 lead, the O only needed to generate a couple of first downs--it didn't have to score--but it couldn't do it, and that gave the ball back to Wisconsin for what turned out to be the game-winning drive. If the offense does its part, the defense has longer to rest and might not even have to take the field again. It's a team game, and too many times in the KF era the offensive team has let the defensive team down.
The same damn thing happened vs. MSU in the 2015 Big Ten championship game, not to mention PSU last year. Just a few first downs at crunch time, and wow, what a difference that would make in Iowa football.