I suspect that you added the calf under the setup tab. To use the Transfer/Foster under the weaning tab, you need to have a birth record. You could setup the real calf's mother under the setup. Record the birth for the calf. Then death the mother to eliminate from your inventory. Then you will have the birth record under the Wean Tab to edit, use the options Transfer/Foster for this new calf. Let me know if still needing help.