Positive commandment · Mitzvat Aseh #78 of 613
To tithe one's herds
לעשר הבהמה
The verse · Vayikra 27:32
וְכׇל־מַעְשַׂר בָּקָר וָצֹאן כֹּל אֲשֶׁר־יַעֲבֹר תַּחַת הַשָּׁבֶט הָעֲשִׂירִי יִהְיֶה־קֹּדֶשׁ לַה׳
“And concerning the tithe of the herd, or of the flock, of whatever passes under the rod, the tenth shall be holy to the Lord.”
The Rambam’s words
To tithe one's herds, as [Leviticus 27:32] states: "And all the tithes of your cattle and sheep...."
לעשר הבהמה, שנאמר: "וכל מעשר בקר וצאן" (ויקרא כז,לב).
Why · Sefer HaChinuch #360
Tithe of pure beasts every year
“It is from the roots of the commandment [that it is because] G-d chose the nation of Israel and wished for the sake of His righteousness that all of them be engaged with His Torah and be knowers of His Name.”
Who & when
“And Rambam, may his memory be blessed, wrote (Sefer HaMitzvot, Positive Commandments 68), “This commandment is practiced by males and females — whether Israelites or whether priests and Levites; in the Land [of Israel] and outside of the Land — whether in the presence of the [Temple] or not in the presence of the [Temple].”
Where in the Mishneh Torah
Hilchot Firstlings הלכות בכורות