Database Performance tanks after mysqldump

Hi all

We have this problem on 2 separate installs.
MariaDB 5.x installed. Once the daily backup is done, the database is almost unusable.

We have TS environments and a DB server - mysql 5.1 running on the TS machines but we have two older sites doing the same and working perfectly.
MyISAM database.

Our batch file runs from one of the TS servers with the following command:
mysqldump -u root -p --databases DB1 DB2 > dumpname_date.sql

Please help friends, this has become extremely oppressive.

Thank you in advance