Can too much spin practice sour a reining horse?

Yes — excessive spinning is one of the more reliable ways to sour a reining horse on the maneuver, and it happens more often than trainers and riders acknowledge because the spin is one of those exercises that feels productive while it is being done even when the horse is past the point of genuine learning. A horse drilled through long spin sets, multiple times per session, session after session, will eventually begin to show anxiety before the spin starts, resistance during the spin, or a general dullness and resentment toward the maneuver that looks like a training gap but is actually the result of over-training. The specific signs of a horse souring on the spin include pinning ears when the spin cue is applied, rushing through revolutions without cadence, hopping or jigging rather than stepping smoothly, dropping the inside shoulder as a resistance behavior, or stopping in the middle of the spin without being asked. Some horses become anxious in the arena generally when the spin has been drilled to the point where they anticipate it every time they stop or slow near the center of the pen. Short, correct sessions are always more productive than long drilling sessions: three to five revolutions with correct form, stopped cleanly and rewarded, repeated a few times in a session with other work between, builds the spin more effectively and more durably than twenty consecutive revolutions that deteriorate in quality as the horse tires and mentally disengages. Variety in the training session keeps the horse fresh and willing — mixing spin work with circles, stops, and other maneuvers rather than isolating the spin as the primary activity prevents the sourness that drilling a single maneuver repetitively produces.