Albert Barnes Commentary Numbers 31:32

"Now the prey, over and above the booty which the men of war took, was six hundred thousand and seventy thousand and five thousand sheep," — Numbers 31:32 (ASV)

Compare Numbers 31:11, and interpret And the prey (that is, the live prey) as meaning “in addition to the spoil which the men of war seized, etc.” The “spoil” is described in Numbers 31:50.

The number of sheep, cattle, asses, and persons taken is given in this and following verses in round thousands. Therefore, the Lord’s tribute (Numbers 31:29, Numbers 31:37–38, etc.), being the 500th part of the half, also results in round numbers. The enormous amount of both livestock and personal ornament was characteristic of the Midianites. When they invaded Israel in the days of the Judges, their wealth was still of the same kind (Judges 6:5; Judges 8:24 and following). The Bedouins, notwithstanding their wild nomadic life, retain their ancestral love of finery to the present day.