Blinding (single and double).

Blinding protects subjective outcomes above all: pain scoring, movement quality and behaviour depend heavily on what the observer expects. A hard outcome such as a laboratory value is less vulnerable. It is worth checking at the end whether blinding held, since a marked side effect or a distinctive smell often gives the group away.

In horses, expectation belongs not to the animal but to the people around it: owner, groom, rider and examining veterinary surgeon. The horse has no idea which treatment it received, yet it responds to changed behaviour in its surroundings. Blinding therefore targets everyone who measures, judges or trains the animal.