Colostrum milk is only produced for a few days
"Human breast milk gives human babies unique immunological defenses that they can't get from other animals milk."
Yes, but only for the first few days (it's called colostrum). All mammals produce colostrum just prior to birth, and farmers know that it's very important to nurse newly-born animals with their mother's milk for just this reason. After that, it's no longer as important and you can successfully use other mammalian milk with human newborns.