From our own experience, not many folks keep up their named.ca or root.hints file for the DNS service. Fetching this file every month is recommended if you run a busy recursive DNS service, for example, an ISP provider DNS or medium to large corporation DNS servers.

You can easily fetch this file with a dig utility:

dig @a.root-servers.net . ns > root.hints

or

dig @a.root-servers.net . ns > named.ca

You can easily set-up a crontab entry to perform file update.

Enjoy!