Related על דמאי 6:5

[In the case of] a cow of a Kohen that was put in a Yisrael’s care [on the condition that the Kohen and the Yisrael share the profits from the offspring] and that gave birth to a firstborn calf, the firstborn calf belongs to the Kohen, the words of Rabbi Yehudah. (Y. Dem. VI.4.3). But the Sages say, the firstborn calf belongs to both of them. Rabbi Yehudah said to them, "Do you not agree that the produce [per Yerushalmi, "tithes"] of the field is his?" They said back to him, "The body of the field is his, and the body of the cow belongs to both of them. Nevertheless, if the body of the cow belonged [solely] to him (i.e., the Kohen, see ibid.), its firstborn would belong to the Kohen."