Musar על סנהדרין 130:1

I have heard about an explanation found in an ancient manuscript: Abraham wrote the ספר יצירה, and handed it over to his son Isaac. Isaac in turn passed it on to Jacob. Jacob passed the book on to those of his sons who were the most deserving. Torah secrets are not supposed to be handed to undeserving people. As a result, only the sons born of Jacob's fully fledged wives were given copies of the book. We find in the Talmud that Abraham created a calf every Friday, by using instructions in the ספר יצירה on how to arrange the various letters in G–d's name in order to accomplish this. Since the brothers had access to that information, they may have done the same thing. Anything which came into being through this method is not subject to the halachot requiring slaughter, removal of blood, etc., before the animal is fit to be consumed. An animal created in such a way may be eaten while "alive." Joseph was not aware of this, hence he thought that what he reported to his father was a misdemeanor by his brothers.