But did you _add_ the module into the initrd?  This should be done in your
configuration file upon which you run `guix system reconfigure`.

  (operating-system
   ;...

   (initrd-modules (append (list "usb_module")
                         %base-initrd-modules))

Also see the info page "(guix) operating-system Reference".

--
Pierre Neidhardt

Reporter:   "What would you do if you found a million dollars?"
Yogi Berra: "If the guy was poor, I would give it back."