In General Entries, Feed, you can use the Type column to tell PigVision that the amount you have entered should be registered as Consumption, Purchase, Inventory or Sale. The default is Consumption. If you choose "Inventory", PigVision will allocate this as the stock of feed left at the end of a period and automatically deduct it from the total for this period and add it into the next period. 

Use purchase if you prefer to list feed by purchase date (rather than show it as being consumed) or sale if you sell the feed to another farmer.