Injuries in the field: How does the mix of mares and geldings play in?

3 min.

Maybe like us, you have always been told that mares and geldings are best kept apart. Supposedly because a mix of genders increases the risk injuries in the field. This is thought to be due to the horses’ aggressive behavior directed at the opposite sex. But is that really true? We have taken a look at some studies of horses’ field behavior.

[adrotate group=”16″]

“There is no greater (or lower) risk in turning horses out in mixed groups than there is in letting them stay in groups of only mares or geldings”

Animal psychologist Nanna Mia Hansen


Does your horse only spend field time with others of the same sex? Then he or she is far from the only one. Most horse people have at some point encountered the myth that geldings, stallions and mares are best off in separate groups. Of course, mares and stallions cannot be kept together for the simple reason that we all know. But does the same apply to mares and geldings?

Animal psychologist Nanna Mia Hansen points out – based on a number of studies, that letting her horse in a fold in mixed gender groups does not affect the horse’s level of aggression or the risk of injuries.
On Facebook profile, she writes: “There is no greater (or lower) risk of turning the horse out in mixed groups than there is of letting them stay in groups of strictly mares or geldings.”
She also writes: “Young horses should preferably grow up in mixed gender and age groups, otherwise they risk becoming socially handicapped.”

We have looked at the research studies that Nanna Mia Hansen refers to. Both studies examine the gender composition among horses in field groups.


The purpose of the study was to test the effects of gender composition of horses in relationship to injuries, social interactions and distance. A total of 66 horses from Norway and Denmark were used for the experiment. They were divided into six groups – a group of mares, a gelding group and a mixed group, where most groups consisted of three or four animals.

After 4–6 weeks of acclimatization, the researchers recorded the horses’ social interactions using continuous observation – 1 hour in the morning and 1 hour in the afternoon for three consecutive days.

The horses were thoroughly inspected for damage beforehand, day 1 after and daily for 4–6 weeks during grouping. No significant differences were found in the horses between the three groups.


Another Scandinavian study from 2016 called Injury incidence, reactivity and ease of handling of horses kept in groups is also interesting. Here, 61 groups of horses from Sweden, Finland and Denmark were used to study gender and aggression. The researchers found that the horses’ levels of aggression were not depended on whether they were stallions, mares or geldings. The level of aggression between the horses was to a much greater extent determined by the breed. An also how much replacement there was in the field.


The Scandinavian study also showed that warm-blooded horses in particular show more aggressive behavior. That is when new horses are to be included in the group – than is the case, for example, with Icelandic horses.

The Icelandic horse was actually the breed that got the most from interacting with each other across the sexes in the study. In other words: should we really be more concerned with the breeds? Or with whether mares and geldings – and stallions – get together when it comes to the behavior of the horses in the field?


Applied Animal Behaviour Science: Grouping horses according to gender – Effects on aggression,
spacing and injuries

Applied Animal Behaviour Science: Injury incidence, reactivity and ease of handling of horses kept in groups: A matched case control study in four Nordic countries
Animalpsykologist Nanna Mia Hansen: Hopper & vallakker kan trives sammen

Related tags

Similar Articles

Content, competitions & community - Straight to your inbox