פירוש על עבודה זרה 31:4

Judah allows Jews to sell maimed animals to non-Jews because they cannot be cured. They will not be able to use them as work animals. The non-Jew will assumedly slaughter them immediately and it is not prohibited to sell animals used for food to non-Jews. The other sages point out that these animals can give birth. Thus a non-Jew may come to hold on to them. Another Jew would then see the non-Jew in possession of the animal and come to believe that it is permitted to sell animals to non-Jews.
Judah responds that maimed female animals cannot be bred. The non-Jew will see this very quickly and will not hold on to the animal for long.