You can now include records of multiple managers for a work item when importing data using the Data Loader.
To import records of multiple managers, in the data file, add the new Link:Managers column and list usernames of managers separated by a comma. The field works similar the Resources and Reviewers fields.
Note: You can only use this field, if the multi-managers functionality is enabled in your environment. To learn more about the functionality, refer to the Multiple Managers for Projects and Work Items article.