MINNEAPOLIS —  The Minnesota Twins have designated reliever Luis Ayala for assignment in the latest move to address their struggling bullpen.

Ayala was 1-2 with a 4.18 ERA in 28 appearances this season. He gave up an eighth-inning home run to Houston's Lance Berkman on Saturday as the Twins relievers let a 3-1 lead slip away in a 6-5 defeat.

The Twins signed Ayala to a one-year, $1.3 million contract in February in hopes that he would develop into a reliable setup man for closer Joe Nathan. But Ayala allowed 38 hits in 32 1-3 innings this season.

The Twins say they bring up right-hander Bobby Keppel from Triple-A Rochester in time for Tuesday's game at Milwaukee.

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