You can record your HGP use by applying it as an animal treatment. In this way you would have a running record of Withholding Periods, Estimated Slaughter Intervals and your Cost of Production.
Adding the HGP into your inventory is the same process as adding normal animal treatments. See our article on Inventory for more information.
Applying HGP as a treatment follows the same steps as your other treatments. See our article on Livestock Treatments for a guide.