Explain how to keep a horse down by placing your knee on his neck and why it works?

Keeping a down horse from rising by placing a knee on the neck is a legitimate emergency and veterinary assistance technique that every horseman working with horses should understand, because the situations that require it arise without warning and require a calm correct immediate response. A horse that has gone down from sedation, a horse being kept down for a ground-level veterinary procedure, or a horse that has fallen and needs to be kept still while emergency help is summoned are all situations where this technique has direct application. The technique works through a specific neurological mechanism rather than through brute physical force. Applying firm downward pressure on the horse's neck — specifically on the upper neck close to the poll — triggers a neurological response that inhibits the horse's rising reflex. The horse's ability to rise from the ground depends on a specific sequence of movements that begins with raising the head and neck. The horse cannot generate the leverage to push his body upright without first elevating the poll and head. Pressure applied to the neck at the correct location prevents this initial head elevation, which prevents the entire rising sequence from initiating regardless of how much the horse's legs are moving. The correct position places the handler kneeling with one knee directly on the horse's neck in the area between the poll and the midpoint of the neck — closer to the poll is generally more effective because it prevents the head elevation most directly. The handler's other knee is on the ground beside the neck for stability. The handler's bodyweight rather than muscular strength does the work — leaning into the neck with bodyweight is more sustainable and more effective than pressing down with arm strength. A blanket, coat, or any soft covering placed over the horse's eye on the uppermost side provides an additional calming effect that complements the neck pressure. Covering the eye reduces the visual stimulation that increases the horse's agitation and urgency to rise, and many horses that are genuinely trying to get up will quiet significantly when the eye is covered and neck pressure is applied simultaneously. The duration for which any horse can be kept down in this manner is limited, and the technique is intended for short-duration situations rather than as a substitute for sedation in any procedure of significant length. Monitoring the horse's breathing throughout is essential — horses restrained on the ground can experience respiratory compromise if the position compresses the chest or the head position obstructs normal airflow.