According to this tweet by Brewers director of media relations Mike Vassallo, RHPs Santo Manzanillo, Josh Ravin and Jesus Sanchez were outrighted to AAA Nashville today, bringing the 40-man roster down to 35.
The big surprise here is with Sanchez. His 2013 season wasn't as outstanding as his 2012, but he still did fairly well in his first full AAA season with an ERA of 2.83, a 1.243 WHIP, and BB/9 of 2.3. His K/9, on the other hand, dropped to 6.4--his lowest since 2010. As to why Sanchez being off the 40-man roster is important, this now exposes him to the Rule 5 draft. You may remember the Mariners claiming LHP Lucas Luetge from the Brewers in the Rule 5 draft before the 2012 season. It's a great way for teams to take a risk on a player and fill holes.
The other players are probably not in any danger of being plucked in the Rule 5 draft. Ravin was a very recent waiver from the Reds and is definitely still a work in progress, with a career BB/9 of 6.1 in 8 minor league seasons. Manzanillo is more familiar to Brewers fans; his constant presence on top prospect lists would have come to an end in 2014 anyway. He was demoted to Advanced A Brevard County midseason in 2013 after putting up horrible numbers at AA Huntsville.