IRVING, Texas -- The look of the Dallas Cowboys’ offensive line has changed dramatically over the last three seasons.

In 2011, the Cowboys started the process of tearing down the line, moving on from Marc Colombo, Leonard Davis and Andre Gurode. In 2012, they replaced Kyle Kosier.

But in stripping down the line, the Cowboys didn’t have ready-made replacements, with the exception of Tyron Smith, who was their first-round pick in 2011. Bill Nagy was an undersized guard and seventh-round pick. He started four games before getting hurt. The Cowboys recalled Montrae Holland to the roster and started him for 10 games. They relied on Derrick Dockery as well. At center, they went with undersized Phil Costa, who was undrafted in 2010. Kevin Kowalski, another undrafted player in 2011, was a key reserve.

This spring the Cowboys have a line with three first-round picks in Smith, now at left tackle, center Travis Frederick and right guard Zack Martin. Doug Free is the only holdover, moving from left tackle to right tackle.

This offseason the Cowboys have stripped down the defensive line. A year ago at this time, Jerry Jones called it the strength of the team. DeMarcus Ware is now with the Denver Broncos. Jason Hatcher is with the Washington Redskins. Jay Ratliff is with the Chicago Bears. Anthony Spencer is coming back from microfracture knee surgery.

“There is an analogy there,” coach Jason Garrett said. “A lot of veteran players, who were really good, of the same generation, and you have to transition. You have to get younger.”

Like the offensive line, the Cowboys didn’t have any ready-made replacements on the defensive line. Instead of going with late-round or undrafted players, the Cowboys are going with low-cost veterans with questions about health, consistency or both.

They added Henry Melton, Jeremy Mincey, Terrell McClain and Amobi Okoye in free agency. They kept Spencer on a one-year deal for short money. They drafted DeMarcus Lawrence in the second round and Ben Gardner and Ken Bishop in the seventh round.

“Defensive line is one of those positions you can’t have enough of those guys,” Garrett said. “Some of the best teams I’ve been around, some of the best teams we’ve completed against seem to have a boatload of these defensive linemen constantly coming at you … We’ve just got to keep them coming.”

Rebuilding is not one of George Carlin’s seven dirty words, but it sure can be viewed that way at Valley Ranch. The preferred word is retooling. The Cowboys have retooled the offensive line. They are in the process of retooling the defensive line.

There might be a question of quality, but there is no question of quantity.

“The best defensive lines I’ve been around are the ones that have ‘wave’ players,” Garrett said. “If you think back to the 90s when this team was winning Super Bowls there were eight legit defensive linemen rotating through games. Jim Jeffcoat playing 12 plays in a game. It’s ridiculous.”

Garrett went on to mention Leon Lett, Chad Hennings, Jimmie Jones, Charles Haley, Tony Tolbert, Tony Casillas and Russell Maryland.

“If you can have some of those guys play 30 snaps instead of 60 snaps or 15 snaps instead of 30 snaps, you’re going to be so much better,” Garrett said.

Nick Hayden played a defensive-line high 821 snaps in 2013 after being unemployed in 2012. Hatcher played 747 in 15 games. George Selvie, who was signed during training camp, played 744. Six of his seven sacks came in the first nine games.

“We played a lot of snaps last year,” Selvie said. “Where the rotation helps is everybody can stay fresh. The new guys coming in, it will help a lot. It was rough by the end of the year. We were hurting. A lot of snaps like that takes a toll on your body.”

To carry out the offensive line analogy, Lawrence can be viewed like Smith, a premium pick at a premium spot. And the job is hardly close to being over. Melton, Okoye, Spencer, Selvie and Hayden all could be on one-year deals. Mincey signed a two-year deal. McClain is on a three-year deal.

“The games are won and lost up front and always will be lost up front,” Garrett said. “If you don’t have good offensive and defensive linemen your skill guys can’t do what they need to do. So we’ve tried to do that. We’ve kind of tried to restructure our fronts over the last few years and build the team the right way.”

The retooling is in its infant stages, like the offensive line in 2011. The Cowboys have to replenish the defensive line in 2015 and beyond with more premium picks the way they have the offensive line.