Christian Buettner-167247 (1/13/2014)
For SQL Server 2008 R2 there is no valid answer, as sys.dm_exec_sessions does not contain the open tran count. But thanks to this, I have learned that this column is new in SQL Server 2012 🙂
You are correct. 2012 is where the open transaction field\count was added to the dm_exec_sessions. But you can get the transaction count in 2008 by joining (cross apply, join, etc.) with exec_requests and cross applying sql_text and query_plan to generate a "monitoring" tool.
However, this is a question I had on one of my tests and believe it or not, they took it directly from BOL and TechNet and I got it wrong because of the open tran count per session.:ermm: