Herrera appeared in only two games for Milwaukee this season, giving up five runs -- four earned -- in 1 2/3 innings.
The 26-year-old left-hander spent his first three major league seasons with the Reds. In 113 relief appearances with Cincinnati, he posted a 3.62 earned run average, and a strikeout-walk ratio of 66-33 in 92 innings.
Rosario, 21, is a right-hander who has not yet made a major league appearance. He has split this season between Single-A Brevard County of the Florida State League and Single-A Wisconsin of the Midwest League.
In 35 total appearances (14 starts), he has posted a 4.32 ERA. In 100 innings, he has struck out 81 and walked 45.