This refers to the way they would count their animals. Alternate translation: "when you count your animals by raising your shepherd rod and having them walk under it to the other side" or "when you count the animals" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This can be stated in active form. Alternate translation: "you must set apart one-tenth to Yahweh" (See: [[rc://en/ta/man/translate/figs-activepassive]])