OpenVPMS doesn't directly support data migration from other veterinary practice systems.
It does however provide a plugin for Pentaho Data Integration (PDI, aka Kettle) that can be used to get data into OpenVPMS.
At this stage, only PDI 3.2 is supported. This can be obtained from here.
Extract this zip file to a directory. This will be referred to as <PDI_HOME>.
To install the OpenVPMSLoader plugin:
See also Implementors Forum|Data Migration
Note that PDI 3.2 needs to use the 32-bit Java JVM. If you have previously installed the 64-bit version for Tomcat to use then you will also need to install the 32-bit version for PDI.