Most adult anythings can't digest milk, western European humans are unusual in this respect. Don't know if ruminants are different, do they have bacteria that produce lactase?
Adult pigs love milk, and it seems to be really good to bring condition back onto recently farrowed sows. My dog has now learned that at the end of the cream separation there is always a bit of cream left inside the centrifuge... well worth queueing up for... No problems with her having milk for he rbreakfast most mornings either...
I have heard of goatkeepers feeding a bit of milk back to nannies soon after kidding to prevent milk fever, I haven't had to do that yet, although I have used Calciject in pregnancy toxaemia and/or hypocalceamia just before kidding.
Mine get a mixture of bran and sugar beet shreds, warm, and the molasses from the shreds go into their drinking water. I would add Caprivite regularly.