Albert Barnes Commentary Leviticus 27:32

"And all the tithe of the herd or the flock, whatsoever passeth under the rod, the tenth shall be holy unto Jehovah." — Leviticus 27:32 (ASV)

Whatsoever passes under the rod - According to rabbinical tradition, the animals to be tithed were enclosed in a pen, and as they went out one by one at the opening, every tenth animal was touched with a rod dipped in vermilion. Compare the margin reference.

For a more full explanation of what relates to tithes, see the margin reference and Genesis 14:20; Deuteronomy 14:22, Deuteronomy 14:28.