daf bit: Bava Kama 95

The mishna teaches: if one misappropriates a pregnant cow and it gives birth, or a sheep and he shears it, he pays the owner the value of a cow about to give birth or a sheep about to be shorn. (That is, he pays the value at the time of the robbery.) In the g'mara Rabbi Meir says he has to pay for the cow and the calf (or the sheep and the wool); Rabbi Yehudah says that the animal is restored intact and the one who took it pays for the calf or the wool. The g'mara goes on to say that this is true if the cow was already pregnant or the sheep was already ready to be shorn; if it entered that state after being taken, then the owner, not the taker, gets the benefit (the calf or the wool). (93b (mishna), 95a, 95b)