Table 2.

Description and illustrations of the selected mutually exclusive behaviour activities.

Activities	Descriptions	Illustrations
Self-grooming	The horse performs body cleaning by himself. It includes: shaking the entire body or a part of it (a); nibbling or licking the coat hair (b); rolling on the ground (c); rubbing parts of the body against objects (d) or other parts of the body (e.g., rubbing the muzzle against the limbs) (e).
Mutual grooming	Body cleaning is performed reciprocally or by one horse towards a conspecific.
Lying	The horse is lying on the ground in the sternal position with the limbs flexed below the body (f) or in lateral position with extended limbs (g).
Playing	The horse plays alone or with other horses. It includes: play with structural parts of the pen (h), sexual play (i), locomotor play (l), and play fighting (m).
Locomotion	The horse moves inside the pen by taking steps; the neck is in a horizontal position (n) or lowered to the ground to sniff (o).
Feeding	The horse eats hay, straw or feedstuff in the trough or on the ground.
Drinking	The horse drinks.
Standing	The horse is in quadrupedal station. The expression is relaxed or attentive. It includes: “standing alert” (p) and “standing relaxed” (q).
Snaking	The horse stretches its neck towards a conspecific with the ears turned backwards, the lips are often closed and the body is in a dominant position.
Kicking	The horse lifts one (r) or both hind limbs (s) off the ground and quickly stretches it/them towards a conspecific, aiming to hit him.
Biting	The horse quickly opens and closes its mouth and its teeth touch the body of a conspecific, aiming to bite him. The ears are turned backwards.
Sexual behaviour	The stallion sniffs or bites the mare’s genitals (t). The stallion mounts the mare: erection and penetration are present (u).
Stereotypic behaviour	The horse expresses a stereotyped behaviour: both oral (v) and locomotor stereotypes (z) are considered.