Someone up thread mentioned it, but the Hay Hut has been a godsend for hay squabbles in our herd of five, that always has a revolving foster or two coming through and going with an occasional rank insecure leader. We used to have a standard roundbale feeder (uncovered) and it was like watching a ceaseless merry-go-round as the horses marched around; the boss would chase the next lowest on the rung, who would then chase the next, and so on, so forth. The Hay Hut completely cut that behavior down.
When to separate is up to the risk tolerance of the owner, the set up/management of the facility, and whether or not the horses truly jive. Sometimes they don’t.
It’s my experience too many people are quick to pull horses from situations before they work things out themselves, which just makes for poorly socialized, ill-mannered horses who spend their whole lives in isolation because no one ever did them the kindness of learning how to interact with other horses. In most cases, a horse that gets kicked put himself in that position – kicking is a close range attack and just about any sound and able-bodied horse should be able to see the signs and move. For many horses it is a last ditch message to “GTFO” - unless the horse isn’t properly socialized.
On the other hand… people pay so much money to keep a horse, and a hurt horse who can’t be ridden doesn’t have much of a future in most parts of the world, so I can certainly understand the intolerance of risk there for many people, who don’t want to see a horse hurt in their care.
Squabbling over hay is usually a management complication. Horses compete for food, or they compete for mares. Occasionally, they compete for space or shelter too – so the smart thing to do is never put resources in an area where they need to compete for them. Put your hay far enough away from other horses, fence lines, or obstacles. The general rule of thumb is to have least +2 additional piles for any horse number over 1 and to space each pile 40ft+ away. Make sure your paddock is truly big enough to house two horses - and if you are regularly dropping hay, drop the hay on opposite ends of the paddock.
This is just my observation having owned quite a few A-hole, insecure leaders – often, I don’t think they are more interested in the other guy’s hay. I think instead, they feel obligated to make the other guy’s feet move – usually because the horse is too close to them for comfort. But the other horse is “that close” because that’s where the hay pile is. So what they do is tell the horse, “this is my spot and my space” – they chase the horse away. The horse keeps returning, understandably, because of the hay pile which is still within Boss Horse’s space bubble. So it’s very important to put these piles of hay very far away from one another so the other horse’s presence can in no way be misinterpreted as a threat to their resources.
If this is the only time they are bickering, consider leaving hay out for them 24/7 versus at scheduled points in time. If they are kept at home this is very manageable, either by a slow feeder or hut of some sort. Horses who only see a few flakes a feeding are way more excited about the hay than the horse that has round-the-clock access to hay.
The other thing you can do, is sprinkle high value grain, fenugreek, or treats over the Boss guy’s hay flake. That will keep them glued for a while.
