Which part about the file handling isn't working exactly (the code looks good at first sight)? Does the text file get written correctly? What gets placed in the list box when trying to load from a file?
If you want to store the animals, even after the program has quit, then there is no other option than storing it in a text file on the hard disk.
If you want to store the animals, even after the program has quit, then there is no other option than storing it in a text file on the hard disk.