A warning, not bad manners
Ears are a horse's semaphore, and ears pinned flat against the neck are the clearest signal in the whole set: a warning that if the message is ignored, the next stage is a threat display, a bite or a kick. It is worth remembering that a horse who warns is doing everyone a favour — he is communicating at the lowest level that usually settles things without injury. Horses learn the manners of their companions quickly, and most ear-pinning between settled fieldmates is over in a second, the lower-ranking horse drifting away and no harm done. Problems start when there is no room to drift.
Read the moment before you judge it
Context tells you what the warning is protecting. At feed time, pinned ears are almost always about resources — hay, a bucket, the best patch of grazing — and a horse who guards food fiercely may have known hunger or competition earlier in life. At the stable door or in a gateway, it is often about space: horses hold a strong sense of their own bubble and object to being crowded through narrow gaps by bolder companions. During introductions to a new horse, expect plenty of it across the first days while a hierarchy is negotiated; that is normal herd business, best watched from outside the fence rather than managed from within it.
Managing the daily flashpoints
Work with the signal rather than trying to train it away. Feed horses who guard with generous distances between piles or buckets, and give the guarder his own space where he does not need to defend his dinner. Introduce new horses across a fence first, with room for both to retreat, and turn out in combinations you have actually seen settle rather than hoping rivals will sort it out under pressure. Where two horses must share a gateway or a water trough, watch the first meetings rather than assuming — a trough placed so a lower-ranking horse can drink without being trapped in a corner removes one of the commonest flashpoints on any yard. In the stable, let handlers know which horse needs his door approached without a companion crowding alongside him. If one horse is persistently bullied — losing condition, carrying bite marks, always standing apart from shelter and hay — that is a grouping problem to change, not a character flaw in either animal.
When pinned ears point to pain
A settled horse who begins pinning his ears at people — at grooming, at saddling, at being caught — is saying something different, and it is worth listening properly. Discomfort in the back, around the girth or in the teeth commonly surfaces as new grumpiness at predictable moments, and a vet check that looks at those areas beats a behaviour label every time. Note when the change began and what it coincides with, because the timeline is the most useful thing you can hand your vet. Sharing those notes in KinsLe through Care Teams means the whole yard knows which horse needs space at the hay pile and which pair should not share a gateway, so his warnings get respected instead of stumbled into.