Comentario sobre Levítico 27:32

תחת 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).

תחת השבט, “beneath the rod.” The legislation to tithe the tenth animal born in one’s flock applies only to animals which were not purchased by the owner of the flock but were born of his flock. The legislation does not apply to flocks owned in partnership either (Bechorot 56). The same halachah applies to the requirement to give the firstborn male animals in one’s flock to the priest. At least this is the opinion of Rabbi Ilai who says that if the mother animal is owned jointly there is no need to give the firstborn male animal to the priest. These opinions are based on the expressions בקרך, “your cattle,” (sing.) and בצאנך, “your flock,” (sing) in Deut. 15,19. If someone had purchased sheep in the market he is not obligatd to either tithe them or give the firstlings to the priest. Our sages in Sotah 27, commenting on Leviticus 22,27, use the various examples named in that verse as the basis for ruling that animals born of animals which crossbred such as a billy-goat with a sheep, or which were not born but came into this world through cesarean section are not subject to this legislation. Such expressions as שור או כשב או עז כי יולד, “ox or sheep or goat which are born,” are all dissected to yield these halachot. Expressions such as “it has to remain with its mother for seven days,” (ibid.) are interpreted to mean that animals orphaned at birth are not subject to the legislation discussed here, all because both here and in chapter 22 the decisive consideration is the animal’s being suitable as a sacrifice at that time. Seeing that an animal whose mother died at birth can never fulfill the condition of spending seven days on earth during the lifetime of its mother and can therefore not qualify as a potential sacrifice, its owner is also not subject to the legislation described by the Torah in our paragraph.

And calves. Because this mitzvah only applies to cattle and the flock as it says, “tithes of cattle and the flock.”