Rashi on Leviticus 27:32/רש"י על ויקרא כ״ז:ל״ב

1תחת השבט [WHATEVER PASSES] UNDER THE ROD — When he is about to tithe them (the cattle), he passes them through a door one after the other and the tenth he strikes with a rod smeared with red dye so that it should afterwards be recognised as being one of the tithe. Thus he does to the young sheep and to the calves of each separate year (Bekhorot 58b).

2יהיה קדש [THE TENTH] SHALL BE HOLY [UNTO THE LORD] — inasmuch as its blood and its fat portions have to be burnt on the altar; the flesh, however, may be eaten by the owner, for we do not find it enumerated among “the gifts of the priests” (Numbers ch. 18), nor do we find in the Torah elsewhere that its flesh should be given to the priests.