Is the value of a lost item assessed at the time it is picked up, like lost sheep, or at the time it is returned to its owner?

Question:
If the finder of a lost item benefits from what he found, such as lost sheep, and then the owner comes looking for it, is the value assessed at the time it was picked up or at the time it is returned to him?

Answer:
At the time it was picked up, at the value it had when it was picked up, because that is the time when he consumed it and slaughtered it.