Between Triple-A Toledo and Class A West Michigan, Downs had a 2.16 ERA over 16 2/3 innings. He owns a career record of 2-3 and has struck out 57 hitters in 56 Major League innings.
With the addition of Downs to the 40-man roster and the removal of Erik Bedard, who filed for free agency on Thursday, Houston's 40-man roster remains at 36 players.
Joey Nowak is a reporter for MLB.com. Follow him on Twitter at @joeynowak. This story was not subject to the approval of Major League Baseball or its clubs.