Leviticus 19:19

Thou shalt not let thy cattle gender — This was prohibited, partly to restrain the curiosity and boldness of men, who might attempt to amend or change the works of God, partly that by the restraint here laid even upon brute — creatures men might be taught to abhor all unnatural lusts, partly to teach the Israelites to avoid mixtures with other nations, either in marriage or in religion, which also may be signified by the following prohibitions.