Horn (elbow) began a throwing progression May 14, MLB.com reports.
Horn received a cortisone shot in mid-April to combat discomfort in his left elbow, which he had scoped during the offseason. The injection appears to have done its job, but Horn could be ramped up slowly in his throwing program after the Tigers pulled him off his rehab assignment earlier this season. He'll eventually head back out on another rehab assignment and may need most of the 30-day window before Detroit brings him back from the 60-day injured list.