The Gemara teaches that an animal that is born from a kosher animal that has the appearance of a non-kosher animal, is nevertheless kosher, assuming that the father was kosher, as well. If, however, the father was a non-kosher animal, the offspring would not be kosher. The assumption that a non-kosher animal could impregnate a kosher animal is questioned by the Gemara –
Can impregnation take place from an unclean animal? For Rabbi Yehoshua ben Levi said: There can be no impregnation either of an unclean animal from a clean animal, or of a clean animal from an unclean animal, or of large cattle from small cattle, or of small cattle from large cattle, or of a domestic animal from a beast of chase, or a beast of chase from a domestic animal, except in the case discussed by Rabbi Eliezer and his disputants, where all say that a beast of chase can become pregnant from a domestic animal.
In response the Gemara explains that the first case was when the father animal was a kalut – it was born of a kosher animal but did not have split hooves.
Occasionally an animal with split hooves will give birth to a creature that has a birth defect – its hooves are not split. Although such animals do not have the usual indicators of kashrut , nevertheless we can be certain that it is from the family of kosher animals. This would be true even if the newborn animal does not have the appearance of the kosher mother, e.g. it looks like a camel or a donkey; since we know that it was born from a kosher animal it is kosher and can be slaughtered. This is not the case where the fetus does not have the appearance of an animal at all, e.g., when it looks like a bird or a lizard.