Who said horses are incapable of giving birth without assistance?
I have a weird guilt reaction when I see animals/pets giving birth because in a weird way I feel like they don't have informed consent to such a painful and crazy thing!
If people can help out to make things go smoother or safer I don't see the problem. I don't know enough to say if they were or were not needed in this instance but everything went well so what is the harm? I don't think the horse minded!
Edit: OMG I'm sorry I forgot to tell you how ADORABLE your baby is!!! It's so nice to be privy to that sort of occasion and hear the excitement and happiness all around! Congratulations!!!