Per Tim. Altoona has room because several guys (Aaron Pribanic, Aaron Poreda and now Kyle Cofield) are hurt. Irwin is no surprise. He was slated for Altoona but aggravated a forearm injury he got in the AFL. He had one outstanding rehab start for Bradenton. Poytress has shot through three levels now after opening in extended spring training. With Dan Moskos pitching poorly at Indianapolis, the Pirates could sure use some lefty relief options.
Update from David: As Cocktails pointed out in the comments, Poytress has tweeted that he is not going to Altoona. He was moved in a "paper move" in order to clear a roster spot so that someone else would be available to pitch. This is no surprise with the extra inning games that Bradenton has played. He will be placed back on their roster probably in the next 3-5 days.