Performance horses face pressure to maintain low body condition scores, but evidence shows that very lean horses experience welfare compromise and reduced immune function.
Performance horse welfare at the body condition interface involves genuine tension between athletic optimization and welfare. Some degree of leanness is appropriate for performance, but very low body condition indicates energy deficiency that impairs immune function, recovery capacity, and cold tolerance. The welfare concern is not leanness per se but energy deficit - horses in negative energy balance experience physiological stress and impaired resilience. Competition authorities that require minimum body condition scores protect horses from being presented lean in ways that impair welfare without improving performance.