Charles Ellicott Commentary Genesis 37:31

"And they took Joseph`s coat, and killed a he-goat, and dipped the coat in the blood;" — Genesis 37:31 (ASV)

A kid of the goats. —Hebrew, a full grown he-goat. Maimonides thinks that the reason why he-goats were so often used as sin-offerings under the Levitical law was to remind the Israelites of this great sin committed by their patriarchs.