The Cubs have had to rely on their bullpen quite a bit lately.

They’re taking some steps to try and alleviate some of that workload.

The Cubs selected the contract of lefty reliever Ryan Borucki and optioning Caleb Kilian to Triple-A Iowa. The move fills the Cubs’ 40-man roster and leaves the Cubs with just 4 starters on their 26-man, big-league roster.

Over the last 5 games, the Cubs have had to rely heavily on their bullpen — they’ve covered 18 of a possible 43 innings in that time and they don’t have an off day until May 11. So, the Cubs are opting to go shorter on the rotation in the short term and deeper in the bullpen. The move also gives the Cubs a lefty in the bullpen, something they were without after placing Brandon Hughes on the IL on Saturday.

Borucki impressed in spring and was one of the last cuts ahead of Opening Day. He started the year in Iowa and was impressive across his first 5 games at Triple-A, opponents were hitting just .200 off him and he had 8 strikeouts in 6.1 innings and a 1.26 WHIP. He struggled in his last two outs, though, allowing 9 earned runs on 8 hits with 3 walks in 2.2 innings.

In 7 games in Arizona, Borucki posted a 0.92 WHIP with 13 strikeouts in 7.2 innings. The Cubs are hopeful that’s the type of results he can produce at the big-league level.

For Kilian, his option comes a day after he struggled against the Marlins, allowing 7 earned runs on 10 hits in 3.1 innings of work.

“That he’s not ready,” manager David Ross said of his assessment of Kilian’s outing. “Still got learning to do, still needs some seasoning.”

He’ll get a chance to do that as he returns to Iowa. Kilian still showed flashes of why the Cubs traded for him in the Kris Bryant deal — he was sitting 94-95 mph with his fastball and hit 97 on his second pitch of the game. But Kilian has had an inconsistent pitching schedule, last week he had his start pushed back a couple of times due to weather and has pitched just once in the 18 days before Saturday’s start.

“I mean the stuff’s there, for sure,” catcher Tucker Barnhart said. “Whenever you have that velo, it makes it difficult on hitters. But both of his breaking balls were really good. Was able to command the cutter after the 1st inning, when we needed it.”

The Cubs will have just four starters in the rotation, but could make a move when Kilian’s turn comes back around in the rotation on Thursday in Washington D.C. Jameson Taillon is eligible to return from the IL on Tuesday and Kyle Hendricks pitched in a rehab start last week.