The prohibition against eating animals whose hooves are divided is found in at least two places in the Old Testament. Of course, they occur in the book of Leviticus which is the book that contains dietary laws.

• Lev. 11:3, “Whatever divides a hoof, thus making split hoofs, and chews the cud, among the animals, that you may eat.”
• Lev. 11:7, “and the pig, for though it divides the hoof, thus making a split hoof, it does not chew cud, it is unclean to you.”

Why is it that God forbade the Jews from eating such animals? Here is a quote that should help.

“Ruminating animals by the peculiar structure of their stomachs digest their food more fully than others. It is found that in the act of chewing the cud, a large portion of the poisonous properties of noxious plants eaten by them, passes off by the salivary glands. This power of secreting the poisonous effects of vegetables is said to be particularly remarkable in cows and goats, whose mouths are often sore, and sometimes bleed, in consequence. Their flesh is therefore in a better state for food, as it contains more of the nutritious juices, is more easily digested in the human stomach, and is consequently more easily assimilated. Animals that do not chew the cud, convert their food less perfectly; their flesh is, therefore, unwholesome, from the gross animal juices with which they abound, and is apt to produce scorbutic and scrofulous disorders. But the animals that may be eaten are those which “part the hoof as well as chew the cud,” and this is another means of freeing the flesh of the animal from noxious substances.”¹Jamieson, R., Fausset, A. R., Fausset, A. R., Brown, D., & Brown, D. (1997). A commentary, critical and explanatory, on the Old and New Testaments. On spine: Critical and explanatory commentary. (Le 11:3). Oak Harbor, WA: Logos Research Systems, Inc.