Regional Jet 900 (CRJ900)
Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Took Evasive Action; Flight Crew Executed Go Around / Missed Approach
Procedure; Environment - Non Weather Related
We encountered wake turbulence from the heavy A300 that was 5 miles in front of us.  We were on a 15 mile right base to 35L at 4000 FT. Once we were cleared for the visual approach we asked the controller if they needed us to maintain a certain speed for separation.  They said speeds our discretion but we were 50 knots faster than the A300.  We began slowing down to approach speed; shortly after we encountered the turbulence. The onset of the turbulence caused the autopilot to disconnect; and the airplane lost about 200-300 FT by the time the event ended.  We immediately told approach control what happened and climbed back up to 4000 FT.  Once we turned final it was clear that the A300 was flying slower than us and 5 mile separation could not be maintained so we elected to go around.The approach controller in SDF had us flying 5 miles in trail of a heavy; at 1;000 FT below his altitude for the same approach. As the smaller aircraft; we would have benefited from having the higher altitude. In addition the aircraft in front of us was cleared for a visual approach before we were; and began slowing before us.  Also there was almost no wind so the wake lingered longer than it normally would.
CRJ-900 Captain reported encountering wake turbulence; while in a 5-mile trail of an A300 on approach to SDF.