EDIT : pour ceux qui n'avaient pas compris, l'auteur souhaite savoir s'il doit mettre une nouvelle arrivante avec son cheval directement ou bien les séparer dans un premier temps
alexsunny123 I don't know if you're aware of it but you're on a French forum so you might have a very few answer in English here...
When my male ( he was a former stallion that couldn't reproduce anymore so we took all the precautions needed) joined my mare and my pony we cut the meadow into two parcels with an electrical fence between each parcel so they could smell and see each other without attacking or anything else.
Two days after his arrival, we put him with the pony and the mare and everything went good.
It also depends on the temper of the horses actually. Some horses would be nice from day 1 whereas some others would attack or refuse any contact with the newcomer