Bechorot 53 - Animal Tithe Today
When one has ten or more sheep, goats, or cows born in his flock in a particular year, he has to give animal tithe. He gathers the animals in a pen and lets them out one by one, through a narrow opening. He counts, and marks every tenth one with red dye, saying, "This one is animal tithe." The tithe animals are brought as sacrifices in the Temple, and are eaten by the owner and his guests in Jerusalem. When there is no Temple, the owner waits till the animals get a blemish, and then he can slaughter them. This is also true for animals born outside of Israel, except that their tithe is not brought to Jerusalem.
Today, however, animal tithes would be problematic, because of multiple prohibitions associated with them. As Rav Huna had described, the farmers used to place the animals' mothers outside the pen, with the result that orphaned and bought animals - from whom tithe need not be separated - would remain inside. The Sages thus instituted not to separate tithes at all, based on the multiple similar situations where the animal tithe would not apply, and about which general population might have been ignorant.
Art: Albertus Verhoesen - A Summer Landscape With Cows And Sheep By A Pool And A Milkmaid Watching