Мидраш к Мишлей 14:4

And Shechem spoke unto his father Hamor, saying: “Get me this damsel to wife” (ibid., v. 4). He (Hamor) went to Jacob and said: Ask me ever so much dowry and gift (ibid., v. 7). And he said: I know that her grandfather Abraham was a prince, but I am also a prince. Jacob replied: He was not called a prince, but an ox, as is said: And Abraham ran to the oxen (ibid. 18:7) and Much grain (can be harvested) through the strength of ox (Prov. 14:4), but you are an ass (hamor), and it is impossible for an ox and an ass to plow together, as it is said: Thou must not plow with an ox and an ass together (Deut. 22:10). The prophet declared: You seek your own misfortune, as is said: The thistle that was in Lebanon sent to the cedar that was in Lebanon, saying: “Give thy daughter to my son to wife”; and there passed by the wild beasts that were in Lebanon, and trod down the thistle (II Kings 14:9).

When your beast eats and is sated, it works the ground with vigor, viz. (Ibid. 14:4) "There is much produce in the power of the ox."