Mike Zimmer likes to rotate his defensive linemen to keep them fresh and feisty. But for much of his first spring as Vikings head coach, his defense has been undermanned up front.

Everson Griffen, one presumed starter at defensive end, stood on the sideline in a bucket hat during part of recent Organized Team Activities because of a minor back issue. Nose tackle Linval Joseph was limited to individual drills after unspecified offseason surgery, so he was held out of harm's way, too. Defensive end Corey Wootton, returning from hip surgery, was being eased into his first week of action with his new team. Meanwhile, Anthony Barr and Scott Crichton, a pair of rookie pass rushers, are across the country, completing classwork at their respective universities.

Zimmer has been trying to get the most out of whoever is present and able to practice, but looking ahead to this month's mandatory minicamp and the start of training camp in July, he believes there will be enough talent and depth on his defensive line to become a dangerous group.

"We will be," Zimmer said. "Once we get the guys that we drafted all in here, I think that will help. Barr will be used a lot of different ways. Crichton will be a rotation guy, I'm sure. And once we get Linval going a little bit more, and Wootton started … we'll start getting a lot better rotation going. Right now, it's just the guys that are out there."

Zimmer's success as a defensive coordinator in Cincinnati started up front with a formidable group of linemen, including All-Pro defensive tackle Geno Atkins and a pair of towering ends in Michael Johnson and Carlos Dunlap. But despite having no defenders record eight or more sacks in 2013, the Bengals relied on their depth — and Zimmer's blitzing — to generate 43 sacks, including 7 ½ from backup defensive end Wallace Gilberry, and they also ranked fifth in the NFL in run defense (96.5 yards/game).

Since Zimmer was hired in January, the Vikings have renovated their defensive line. They let Jared Allen and Kevin Williams walk — although Williams said in a recent Sirius XM radio interview that the Vikings "might be trying to ease back into the picture" — and instead paid big bucks to re-sign Griffen while also adding Wootton in free agency. They drafted Barr, an outside linebacker who will line up as an edge rusher on passing downs, and a pair of linemen in Crichton and Shamar Stephen.

McKenna Ewen — STAR TRIBUNE FILE, Star Tribune
Minnesota Vikings defensive tackle Sharrif Floyd.

"I think we have some guys that can rush the passer," Zimmer said.

Barr and Crichton are getting instruction from afar because NFL rules prohibit them from practicing with the Vikings until mandatory minicamp, when classes at UCLA and Oregon State have concluded. Position coaches have been talking to them via video online and Zimmer's son, linebackers coach Adam Zimmer, flew out to see Barr over the weekend, but there is no classroom like the practice field.

Yet somehow, defensive line coach Andre Patterson had enough big men to coach up, asking two foursomes of defensive linemen to take turns giving his blocking dummies whiplash.

Eighth-year defensive end Brian Robison likes what he has seen so far from his able-bodied peers.

"We're competing with each other," he said. "Guys are working really hard and that's always a good thing during these spring days because guys can easily shut it down and go through the motions."

Robison said Zimmer hasn't explicitly told his players if he plans to rotate them like he did in Cincinnati, where eight Bengals linemen played at least 130 defensive snaps in 2013. But knowing Zimmer's track record, Robison certainly expects that conversation to take place.

"It's one of those things where we have to be prepared for it, but at the same time I'm going to be preparing as if I'm playing 100 plays a game," Robison said. "Really, it's up to them."

All draft choices signed

All 10 Vikings draft choices are under contract following the Tuesday signing of third-round pick Jerick McKinnon, a running back from Georgia Southern.

McKinnon was a triple-option quarterback at Georgia Southern before switching to running back his senior season. He also got snaps at cornerback and wide receiver. He is in line to back up Adrian Peterson this season.