Merklinger, 25, posted a 3.65 ERA in 143 minor league innings last year, mostly at Class A. Overall, the 2007 sixth rounder struck out more than a batter per inning (9.3 K/9) and limited his walks (2.8 BB/9).
Estrada, 27, will start for the Brewers against the Braves tonight. He has an 8.04 ERA in his 31 1/3 big league innings with an impressive 32 strikeouts. He pitched well enough this spring for manager Ron Roenicke to add him to the rotation, at least for now with Zack Greinke sidelined.