You'll need an additional account to record your commissions or any additional fees. This expense/income account will sit within your accounting software.
Recording it via Figured
When you add a purchase/sale into Figured, you'll add your livestock information as you would normally and then add a non-stock line.
In that section, you'll select your newly created account and then add any financial values - enter these values as a negative number if you had to pay money or as a positive number if it was an additional income.
That will then flow through to your accounting software!
Recording it via your preferred accounting software
You can also do the same in your accounting software - raise an invoice for your livestock, then add a line using your new account. Then you can reconcile your livestock information as normal.