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