I read this story about 15 or 20 years ago, not 40 as many of my other questions. But the SF collection it was in might have been much older. It is either a longish short story, or a shortish novelette, difficult to remember exactly. (There is no tag for this ambiguity, I had to use "short story" but it might be too long to be one, technically) Is does not really look “politically correct” by present standards….
The main character is a human. The story might just take place on Earth, but most probably on some other planet. His employers might be human themselves, or possibly aliens, but they recognise him as fully sentient.
When he meets his charges for the first time, he is rather surprised : they look exactly like human women and they are kept for providing milk. However, when looking in their eyes, he realises that they are not human slaves, but really animals with no more intelligence than cows.
He is supposed to feed them, keep their stalls clean, milk them (probably not by hand, just connect and disconnect the milking machines), treat them when they are sick or hurt. And he finds it a rather nice job.
Once he sees a “bull”, a fierce thing in a stall just for him(it?)self, looking like a fine element of human male, but with just lust, frustration and rage in the eyes, but no intelligence. But the "bull" is too dangerous for an ordinary stablehand like our character, they have specially trained people for dealing with him(it?).
I think that at the end one of the “cows” is ready to give birth when he is alone on duty. He manages to deal with that, and brings to the world a nice human “calf”, and he is very pleased by this accomplishment. I don't remember any more "momentous" end, the emotional scene of the successful delivery was just the final climax.