As the tails of the sheep are very large and fat, in those eastern countries, and were considered as a very choice part of the animal, they were ordered to be sacrificed on the altar. Exodus 29:22.
Related Commentaries of Leviticus 3:9
Leviticus 3:9
9 And he shall offer of the sacrifice of the peace offering an offering made by fire unto the LORD; the fat thereof, and the whole rump, it shall he take off hard by the backbone; and the fat that covereth the inwards, and all the fat that is upon the inwards,