Social organisation in herds of horses

The family herd, also known as a « harem », is generally composed of one stallion, between 2 and 4 mares, and youngsters up to 2- 3 years old.

Some harems have two stallions, in this case there is an established hierarchy between them.

The adult horses are the hard core of the harem. As they grow up, younsters are generally excluded from the group :

• Young mares will often leave the herd when they first come into season (around 3 years old in free-roaming conditions) to join a bachelor male or another harem. They may remain in their original harem, especially if the head of family stallion is not their sire ;
• Young males leave the family herd at around 2 to 3 years old, either of their own accord or forced to do so by the head of family. They will then join a bachelor herd.

Horses are very attached to their vital domain, but do not defend it so to speak : the vital domain of different harems can therefore overlap.

The size of the vital domain is very variable and depends on the availability of resources : the more abundant the resources (water, food), the smaller the domain. Vital domains have thus been observed as being from 1km2 to 80km2 ! Their size also depends on the seasons, as the availability of resources is modified.

(1) linear hierarchy : A dominates B, B dominates C, therefore A dominates C

In most family groups, the dominant individual is usually a mare, it is rarely a stallion. Adults are dominant over younsters. See a description of signs of dominance in the fact sheet about the horse’s social behaviour.

In the herd, hierarchy is most often linear (see definition in the previous paragraph), young males being dominated by older males.

In free roaming conditions, groups generally avoid getting close to one another. However they often share at least part of their vital domain, and can therefore be in a position to interact. Harems are usually closer to one another than to bachelor herds.

When different groups use a same restricted resource (e.g a water point) a hierarchy becomes established between groups : the dominant family group will have first access to the resource.

In a configuration where resources are plentiful, individuals from different groups sometimes come together, but will tend to ignore each other despite physical proximity. Their grouping then seems to constitute a form of defense against predators.

In groups of mares or mares and geldings, hierarchy is distinctly linear. This hierarchy is dependant on age, seniority in the group and sometimes weight. Gender appears to be of no importance.

In groups of young horses, behaviour is different from that observed in young horses in family groups in semi-roaming conditions. In several French studies, it has been demonstrated that the addition of one or several adult horses to groups of young horses contributes to increasing friendly behaviour between younsters and decreases aggressivity. This is beneficial immediately after weaning

The consequences of this social structure are numerous when managing horses in domestic conditions. See fact sheet « How to organize and manage groups of horses. »