Whether you keep your horse at home or at a boarding facility, there will be times when new horses must be integrated into an existing herd. Generally, this involves a lot of posturing between the horses– chasing, biting, and hooves flying. Horses take this event quite seriously and it’s a scary proposition to the new horse and its owner.

Horses are herd animals by nature; they form bonded relationships within the herd, vie for status and fight amongst themselves. Acceptance of a new horse is never granted easily by the herd and the addition of one new individual can totally disrupt the hierarchy of the herd. 

The more you understand the horse’s herd instincts, and the ways that domestication complicates matters, the easier it is to make smart decisions. Taking the time to introduce horses slowly and strategically will help the integration of the ‘new kid’ go smoothly, reduce the risk of injury and keep fireworks to a minimum. 

Herd Dynamics

Horses are instinctively gregarious animals, meaning that by nature, they’re drawn to the herd. A horse banished from the herd will always seek acceptance in another herd, because his survival is at stake. A horse is dependent on the herd for its own safety and comfort.

Gregarious behavior is present in all horses, it’s one of their strongest instinctive drives, although we often speak of it as an affliction (herd bound, barn sour, nappy, etc.). Although a horse without a herd will always seek acceptance into a herd, the existing herd always rejects a new member, until the new horse proves it is worthy of acceptance. The new kid is guilty until proven innocent.

A horse herd has a distinct structure and hierarchy of leadership. What horse owners often refer to as the “pecking order,” animal behaviorists call a “linear hierarchy.”  Simply put, every individual in the herd is either dominant over or subordinate to every other herd member. There is no equality in a horse herd; there’s a horse at the top, and one at the bottom, the rest are lined out in-between. Even amongst bonded individuals (buddies), one of them is dominant and the other is subordinate.

The most dominant horse often becomes the leader of the herd and this horse is designated “Alpha.” The next horse in the line of hierarchy is called “Beta.” The horse all the way at the bottom of the pecking order is designated “Omega.” Truly alpha horses are strong, fair leaders that the other horses admire and feel secure in its presence. Alpha individuals may be male or female, an unusual trait in the animal kingdom. Beta horses tend to challenge authority and may act like bullies, but often do not have the leadership qualities of a true alpha horse. The omega horse usually accepts its fate at the bottom of the hierarchy, it rarely challenges authority and tries to stay out of the fray.

By nature, horses are born with a temperament that may be high or low on the scales of fear, confidence, curiosity or dominance, among other traits. A horse is born with its temperament, which will largely dictate where it sits in the hierarchy. But horses are extremely fast learning animals as well; they may learn to manipulate other horses to gain more status. Sometimes horses gain status in the herd from an affiliation with another horse, so adding or subtracting one individual can often disrupt the hierarchy.

An existing herd is always reluctant to accept a new member, unless and until it shows contrition and a willingness to respect the leadership and be a good citizen in the herd. As predictable as the tides, when a new horse seeks acceptance into the herd, the existing herd members will aggressively drive the horse away, as if to say, “We don’t like you and we don’t want you.” 

The new horse continues to seek acceptance, feeling as if his life is dependent on being accepted. He lowers his head in a contrite and subordinate posture, as if to say, “Please, I’ll do anything if you let me in. I’ll follow the rules, respect the hierarchy and be a good herdmate.” 

Eventually, the existing herd members will back off and allow the new horse provisional membership in the herd. The new kid will work his way up the hierarchy to its rightful place and may become bonded with other herdmates. 

Relationships are Complicated

In a stable herd of any size, feral or domestic, the horses all know their position in the herd and are accepted members. Large herds of horses usually have factions, or smaller sub-herds of horses that like to be together.  

Within a large herd there are horses that like each other and others who do not; there are friends, rivals and enemies. Horses prefer to hang out with their buddies and bonded horses will have each others’ back. There are many cooperative and philanthropic behaviors that occur between bonded horses, including protection and fighting off an aggressive horse.

Within any herd of horses, individuals may form a specially bonded relationships with one or two other individuals. In natural herds, bonded individuals (who behaviorists refer to as “associates”) are often related by blood. Stallions can be extremely possessive of mares and entirely hostile towards marauding stallions. 

Horses in the herd, either domesticated or feral, can be possessive of some horses and jealous of other horses.  Sometimes domesticated horses may become possessive over their humans and are jealous or combative if another horse approaches or gets attention from its human.

Forced Marriages

In domestication, horses don’t get to choose their herdmates. Usually humans make that choice, organizing herds according to their own convenience, often without regard to the horse’s natural behavior. Consequently, the horses may not like each other, sometimes bullies are in charge and/or the hierarchy can be unstable. Often, adding or subtracting one individual can change the herd dynamic in surprising ways, because there were false or forced relationships to begin with.

There is never a void of leadership in a horse herd, either domesticated or feral.  If the alpha individual is suddenly removed, another horse will immediately step in as alpha—theoretically, the strongest natural leader emerges, either male or female. 

But what happens if none of the horses in a forced herd are natural leaders? What happens when there are multiple beta horses, all scrapping for dominance? In domestication, although there will always be a leader in the herd, it may not always be a good one. 

Geldings, although neutered, can often display stallion-like behaviors when it comes to possessing mares, fighting off other geldings and even mating. Of course, mares are usually not neutered and therefore may display unpleasant behaviors in estrus, wreaking havoc in the herd for a 4-5 days every few weeks. Interestingly, in feral herds, the mares usually only come into heat once a year, shortly after foaling, then are pregnant again for the remaining 11 months of the year. Domesticated mares that are not bred may cycle most or all of the year, causing a lot of frustration and angst in the herd.

Many large horse operations segregate horses by gender, to avoid the unpleasantness of a mixed-gender herd. I’ve seen it plenty of times—a large group of geldings co-existing peacefully, and the same of mares. But put one gelding in the mare pen or one mare in the gelding pen and there’s kicking, squealing, chasing and hair flying. But for many horse owners, segregating horses by gender isn’t a realistic option.

Even horses that don’t like each other may become a tight-knit herd, when that’s their only choice. But they may never become bonded associates. A horse’s preference or disdain for another horse can be hard to know in a small, forced herd where they have no choice but to hang out together. In larger herds, it may be hard to know which horse are enemies because horses that dislike each other don’t have to interact. 

A manger of a herd of 200 saddle horses once told me that they bought about a dozen horses a year and those horses were quarantined together, then at some point, integrated to run with the larger herd. Because the horses were quarantined together and then were pitted against the whole herd as the “unwanteds,” they often became their own faction, staying together as a sub-group for the rest of their tenure at the ranch, as if that traumatic experience had bonded them for life.

Relationships between horses can be complicated and the preferences or disdain they show for others can play out like a B-rated soap opera at times. This makes integrating new horses into a herd a huge challenge. It pays to be very deliberate, move slowly and test the waters carefully, so horses don’t get hurt.

Flight or Fight

Flight is the most defining characteristic of the horse, a trait that made the equine species difficult to domesticate some five to ten thousand years ago. Horses generally choose flight over other options, but when motivated to fight, they are very well equipped. 

Horse fights are extremely violent, and stallions may even fight to the death. In a normal herd setting, horses constantly make threatening gestures to others or lash out with a kick or bite. Minor horse-on-horse aggression is normal; but if the herd is in a constant state of argument and aggression, some rearrangement may be needed.

A horse has three weapons in his arsenal—his teeth, his front feet and his hind feet. Biting, striking and kicking are the horse’s arsenal and his teeth are his most deadly weapon. When horses fight to kill, they generally bite the jugular. Consequently, when male horses spar, or play-fight, they often bite at the throat.

It’s important to distinguish between aggressive kicking and defensive kicking—most often it’s the latter that we see. When a dominant horse attacks a subordinate, the subordinate kicks out in defense, often with one leg, and then runs away. The kick buys him time. 

Aggressive kicking is typically accompanied by squealing (a terribly loud scream) and the horse is usually kicking double-barrels and backing into the other horse (who may be doing the same). Horses kicking butt-to-butt are very serious about the fight and this is a very dangerous situation.

When two unfamiliar horses meet, they generally come nose-to-nose and smell each other’s breath, then go nose-to-genitals and smell there before coming back head-to-head. At that point you may see aggressive posturing (raised neck, arched back, swishy tail, stomping) and hear a squeal, which means aggression may ensue. 

Any result is possible when two unknown horses meet: they may be indifferent to each other, like each other, hate each other or want to kill each other. Most often, horses are indifferent or get along. When they don’t, sparks may fly and horses may get hurt.

Mitigation Techniques

Introducing a new horse into a herd is best done slowly and with calculation, to minimize the risk of injury. There are so many variables in the herd size and dynamics, the facilities available and the temperament of the horses, that it is difficult to offer suggestions that work in any situation. But over the decades, I’ve learned some tricks that may help ease the transition.

First, I like to quarantine the new horse for a week or two. Not only does this help reduce the spread of illness, it also allows the horse time to get used to his new environment and become acquainted with his new human family. It allows me time to get to know the horse and evaluate his temperament before introducing him to the rest of the herd. 

Next, I like to let the new horse be in a pen that shares a common fence with the herd. I want the fence to be tall (at least five feet) and solid (to hold up to kicking, striking and leaning on both sides). I may only do this for short periods while I observe what horses are friendly and which are aggressive. I may leave the new horse next to the herd for days, as he gets to know the players.

Since more horses are friendly than aggressive, chances are good that some of the horses in the herd will be interested in making friends with the new horse. As I observe the initial interactions over the fence, I can determine which horses will be jealous or possessive and which horses are interested in the new horse. 

If I can, I will allow the new horse to meet one or two of the friendly horses without the fence in between—turning them out together for some time before introducing the rest of the herd. That way, the new horse may have a friend when he meets the whole herd. Sometimes it’s feasible to add one horse at a time to the new horse’s pen, until the whole herd is together.

Often, identifying the one dominant horse that is causing the conflict and removing that horse from the equation, allows everyone else to get along just fine. I would keep that horse isolated from the herd for a week or two, while the new guy settles in and finds his place. Be careful not to break up alliances in the existing herd, as you introduce the horses one at a time. A jealous, dominant horse may come uncorked when he sees his BFF with the new guy.

If I have any concerns about aggression when I put the horses all together, I’ll recruit help from one or two friends. Armed with training flags or whips to wave and make noise, we’ll referee the first meeting. If the horses become aggressive, we’ll shout and wave the flags to break them up and then remove the trouble-makers. A little solitary confinement may make the aggressive horse rethink his behavior next time, while the new horse gets comfortable with the rest of the herd. Fighting horses are scary and dangerous, so proceed with great caution. 

Most importantly, take your time when integrating a new horse into a herd and employ a strategy. Do your best to know the temperaments of the horses and who the main players will be. Most of the time, horses will work out their differences and find a new order in the herd, in a matter of hours, but occasionally, horses can be injured. Whatever you can do to reduce the risk and stress level, will help the horses.

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