I have 3 mares, a gelding, 2 weanling fillies, and a stallion in the same pasture, please note the stallion and gelding have been together since the stallion was a yearling and have been together for about 11 yrs now. I have no problems, the stallion and gelding are buddies, they play hard but don't hurt each other, one of my mares is alpha she runs the herd, the stallion bows to her. My gelding is a paint and my stallion is an Icelandic, the gelding is 2 hands taller and outweighs the stallion by about 400 lbs. The Icelandic is much stronger than the paint and if there was a real fight the paint would lose. My gelding is no threat to the stallion. My old cowboy neighbor thinks I'm crazy for this arrangement, thinks all stallions should be housed separate and only let out to hand breed. I personally believe a happy stallion is a less dangerous stallion, they are herd animals and need the interaction with the herd. I did have them separated for a short time and it cost me a fortune in panels, my stallion would just destroy them to get back with his buddy. This may be a rare exception, I can ride this gelding with my other stallions without issues, but I couldn't pasture them together.