At runtime, shared objects have to be found in the file hierarchy; as usual, there's a search path for that. If more libraries are installed, the search path has to be extended. The way this works under FreeBSD is at follows.
Look in /etc/defaults/rc.conf; you'll find, among other things, the entry.
ldconfig_local_dirs="/usr/local/libdata/ldconfig"
This variable states in which directories libraries can drop files with additional contributions to the path. The format of these files is absolutely simple---just add one directory per line.
As almost everything on FreeBSD, the search path can be updated with
/etc/rc.d/ldconfig restart