After that, I put the new horse back in his original paddock but put the more settled gelding in with him. No serious problems, the older horse would posture a bit if the yearling got too close but nothing unusual. However, after what I saw from this older mare (I think the 2 yr old filly was just joining in because she saw her Mom doing it), I'm wondering if I'm going to be able to let them all into one pasture or not? A friend suggested putting the older mare into a round pen and working her for a bit, then add the yearling and work them aggressively together. His theory was that giving them a "common" problem to handle (me) would help them bond and take the mare's mind off chasing the new yearling.
I really need to get them all in the same pasture as soon as I can for grazing rotation purposes. And, it's crossed my mind that I might have to find the new horse another home but I'd rather exhaust every effort before I take that step.