I had a big post written (including photos) and it disappeared into web space ...
The jist of it being, I have seen successful "bachelor" groups done by other breeders, and I generally do try to keep stallions with other stallions or geldings whenever it is possible. IME I have had a lot of success, but it doesn't always work out.
There are a lot of factors and management that go into it though, and at the end if the day you need to ask yourself if it's right for you and your individual horses.
I have one guy here right now who has a pony gelding who is his buddy - that pony is the only male horse he seems content to live peacefully with, and there have been times (in early spring) where I have even separated them because the play was getting too serious. (It's all fun and games until someone goes too far)
I choose to try to keep stallions with geldings/studs, especially when they are young because I fully believe it is best for their mental health - but I don't blindly throw random horses together, I keep them on LARGE acreage, I don't house mares nearby, and I am always prepared (with extra help) to separate and keep them alone. Once they become mature, and/or have been bred, I keep a close eye on them and will separate when it is noted that there are more territorial postures happening.
I have noted that a well socialized colt generally makes the best candidate for bachelor grouping... But even then, dynamics can change once he starts breeding.
If you choose to try... Get to know your stud well first, ensure he sees you as supreme boss - that alone has allowed me to break through hormones in cases where the boys need separating. (When it is ingrained in a horse's mind that when you show up and give a command, he MUST listen) NEVER get between two fighting horses, and always be prepared for the horses to have other ideas about what makes a good buddy.
I can add more later when I get back from playing with my horses.
Posted via Mobile Device