What is Bog Factor?

Essentially Bog Factor is a component of the Formline rating and is a bonus or penalty expressed in kilograms or points given to each horse according to its career statistics on combined Slow and Heavy track runs. 

If you don't use Formline, you can ignore it within GTX. Make sure it is turned off and not altering your current ratings/prices (figures should be grey as in the image below and then remove the column).