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While it can be fun to see horses kicking up their heels on the spring grass, it’s less so when they start kicking each other. Disagreements can soon get physical. More than half the traumatic injuries investigated in a recent study occurred among horses out in fields, with the possibility of injury at its highest in those joining a new herd.

Most of us witness some kind of pecking order when we turn our horses out in a group, in which one horse appears to be the boss and others rank beneath the leader in order of importance. The term “pecking order” was first used nearly a century ago to describe the dominance hierarchies among hens when grain was thrown down. Hen number one was dominant over hen number two, and so on. This allowed scientists to work out where each individual stood within the group.

This is not how it works with horses, however, as their social order is much more complicated. Horse number one may be able to displace horse two to gain access to a resource such as the haylage bale, and horse two may in turn displace horse three — but horse three may be able to displace horse one.

When you consider another resource such as shade or the water trough, the order may be completely different again.

Scientists have been unable to work out clear ranks in equine groups. There’s no linear pecking order from top horse to bottom: instead, these complex hierarchies have led scientists to describe equine relationships as being on a bilateral level rather than ranked.

Herd dynamics

To understand herd dynamics better, it is worth considering a few interesting points:

• Motivation for a resource can lead to behaviour we might not expect, based on previous encounters. For example, one horse may normally be displaced by all the others in the group for most things — so people assume he is bottom of the pecking order. If a new bale of haylage is placed in the field when he is hungry, however, he may displace other horses to whom he would usually be subordinate.

• In feral herds, safety is prioritised. Individuals soon work out who can displace who, so aggression is only ever seen in two circumstances: between stallions fighting for mating rights and from mares that are protecting newborn foals.

• A foal will often form closer relationships with offspring from his dam’s close associates. A foal from a mare that will displace most others in a group is also more likely to be able to displace most other horses when he grows up, while the offspring of a subordinate mare will probably follow in her footsteps.

• In large groups, horses tend to form closer relationships with those of a similar age. Gender, height and even breed and colour can play a part, but seem to be less important.

• Horses have an innate need to interact with other horses, with behaviours such as allo-grooming (mutual back-scratching) being especially important for wellbeing. The Swiss National Stud now turns all its stallions out together over winter (with no mares around!) to allow them to interact — some great videos of the first time they did this can be found on social media. After some initial snorting and squealing, the stallions were soon living together as a peaceful herd. The stud has now developed social housing for summer, where stables feature vertical bars to ground level to allow the stallions to groom and play safely.

Friend or foe?

The process of integrating a new horse into an already established herd should be gradual.

Ideally, start by turning the newcomer out in an adjacent field so that he can meet the other horses in safety over the fence. If this is not possible, place horses in neighbouring stables so they can interact. After a few days, you may notice the horses at pasture allo-grooming over the fence. The new horse can then join the herd.

If horses have been stabled overnight, try not to introduce a new horse first thing the next morning when they are most likely to want to run around. Avoid adding a new resource, such as a bale of haylage, on the first day.

Injury risk within herds can be reduced by following some simple steps. One of the most important is to keep things constant, because the continual coming and going of horses in a large herd is a recipe for disaster. Turning them out in pairs or small groups is preferable if you are at a busy livery yard with a high turnover of horses.

Given enough space and time, horses will usually settle and sort out their differences. This does mean giving them plenty of room, however — so that if one horse is displaced by another, he can move far enough away to avoid any further trouble — and looking out for any picked-on individuals who may be losing condition.

Mares and geldings should be kept in separate groups. Most injuries in domestic field-kept horses are related to supplementary feeding, so be careful when offering limited resources such as hay where grass is scarce.

Your horse’s lifestyle will have a bearing on how he behaves in the field. Horses are highly social animals, so being kept in isolation from others can, over time, result in an individual losing ability to interact safely with others when he is turned out. His owner is then even more likely to want to keep him in isolation to prevent injury.

Social interaction should begin in early life. A foal needs to learn how to behave with others — keeping him with only his dam in the first few months will not set him up for successful interactions with new horses in the future. His ongoing education should be based on the principles of training, as horses with poor training regimes can become neurotic and are more likely to be aggressive with others.

Another point to consider is “post-inhibitory rebound”. A horse that’s deprived of a resource he has an innate need for is more likely to overdo things when he has access to that resource again.

Post-inhibitory rebound can occur with a horse on box rest but also with one stabled for very long periods. When at last he is turned out, he will feel the need to run and play at a very high intensity. Horses that live out full time — or at least for most of the day — are generally much calmer and less likely to be injured.

Ref Horse & Hound; 11 May 2017