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If you’ve ever watched an unfamiliar horse try to gain entry into an established herd, you will probably never forget it. The violence of the herd members as they pursue the newcomer can be frightening. And yet this is all completely natural behavior that, if you heed the whys and whats of herd dynamics in managing the introductions, needn’t cause more than passing disruption.

In Search of Stability

As commodities and competitors, horses have always been subject to relocation. Now, in our increasingly mobile society, we move from place to place, dragging our horses along with us and expecting them to adjust to new surroundings with ease. But horses place considerable trust in their herds and their “home territories.” Imagine how it feels for a horse to be uprooted from a place of security and plentiful food, of preferred associates, as horse friends are called, and a well-defined place in the hierarchy, to be dropped somewhere completely unknown to him, where at worst a hungry carnivore could already be stalking him and at best a herd of venom-spitting horses stands just across the fence.

The outsider is not the only one affected by the change: During the several weeks following the introduction of a new herd member, the other horses have to redefine their hierarchy to make a place for the stranger. This momentary uncertainty in the social rankings may be the perfect moment for an ambitious young horse to challenge the system, or it may be such an unsettling time that usually docile horses battle fiercely to protect their long-held social rank. Not only does the risk of injury skyrocket, but the turmoil, in general, can be quite stressful.

As with people, stress can debilitate horses and make them vulnerable to infectious illnesses. The risk of viral and bacterial diseases greatly increases in mobile populations of horses. The newcomer might bring in a disease the other horses have no immunity to or inoculation for, or the herd members and environment might harbor infectious organisms against which the new horse has no protection.

The Gender Factor

One of the most obvious results of domestication is the introduction of a new gender of horse: the gelding. Yet, says Katherine Houpt, VMD, PhD, domestic herds containing a mix of geldings and mares may faithfully enact the instinctive sexual displays and behaviors seen in truly wild herds. “Sex isn’t a big issue in the day-to-day life of feral horses,” explains Houpt. “In the wild, all horses are rendered neutral by the fact that most of the time the majority of mares are pregnant.”

But unbred domestic mares spend a good part of the year cycling in and out of estrus, and in mixed-gender herds, sexual pressures may heighten an established group’s hostility toward outsiders. “So many geldings don’t realize that they are geldings,” Houpt says. “The main problem is not that they are showing sexual behavior but that they are being aggressive to other males. If a new gelding shows stallion-like behavior when he’s introduced to a herd, that may cause him to be rejected.”

And then there’s the not insignificant concern about the physical hazards to battlers and bystanders posed by these stallion-like fights.

For the good of the entire herd, a sexually aggressive gelding is best kept only with other geldings and away from mares. “The gelding’s sexual behavior is both innate and learned,” says Cynthia McCall, PhD. “If a gelding was gelded a little late, say after four or five years of age, he might herd mares, fight with other geldings and mount mares.”

Aggression may be present in single-gender herds. Mares may threaten each other to establish dominance but usually stay relatively calm. Geldings will play rough, even when kept apart from the mares but they usually aren’t a serious danger to each other. If necessary, one quiet gelding can be kept with a herd of mares without causing a problem, and of course, a stallion can be kept among mares, with the obvious consequence.

The Cost of Confinement

Although their wild ancestors had unlimited acreage to roam, domestic horses are confined to much smaller areas. Their nutritional need to roam may be reduced because food is there for the taking, but the mental need remains. Freedom of movement is essential to horses’ physical and mental well-being, and entrapment in small spaces is a naturally fearful situation for them, as you may have discovered when a cornered horse decided to escape the threat by running around or over you.

Containment increases aggression among herd members and fuels a generally higher level of anxiety within the group. In overcrowded situations, near-constant bickering or outright brutality occurs over who gets what and when of the basic necessities and the amenities. Introducing newcomers to herds kept in restricted spaces is an invitation to injury, as there’s no room for escape from aggression.

Health problems are exacerbated by confinement, as well. In addition to the increased risk of stress-induced ailments and contagious disease, too-close company ups the probability of parasite infestation. As the number of horses per acre increases in slipshod management situations, so does the concentration of parasite eggs and larvae in pastures and paddocks. A “clean” horse coming into a highly parasitized herd is bound to suffer, and, conversely, a heavily infested horse taking up residence in a closely confined but clean operation is likely to infest the others.

The Social Graces

With domestic horses, weanlings are often separated from their herds before they have a chance to learn proper socialization skills. In the wild, colts stay in the herd for up to three years before leaving to form “bachelor herds.” The members of a bachelor herd roughhouse with each other as practice for the battles they will eventually fight to steal horses from established herds. Fillies leave at about two years of age, presumably to prevent inbreeding with their fathers. They are eventually taken into other established herds or join up with bachelor stallions. In other words, young feral horses get two or three years of training in the workings of herd society before they reach maturity.

Domestic youngsters, on the other hand, are often deprived of these important learning opportunities. Removing a weanling from his herd of birth at four or six months of age may confound his acquisition of “interpersonal skills.” Some horses are forced to lead solitary lives for long stretches and then are thrust into herds and expected to know how to cope. Racing and show stables, where horses usually spend most if not all of their time in stalls or turned out alone, can be breeding grounds of socialization problems.

Buttermilk, for example, was an ex-racehorse who lost a succession of homes because of his savagery to other horses when he was turned out to pasture with them. Even when in his stall, he spent most of his time trying to attack his neighbors. Yet when isolated, he fretted himself sick about getting back with the others. Stymied but determined to teach Buttermilk to play nice, his last owner “fed” him another horse. Buttermilk ran his new pasturemate around the field for about a week, peppering him with bite marks. Day by day they slowed down, until finally Buttermilk was “chasing” the other horse at the walk. Eventually the two did become friends, and both were turned out with the larger herd. Three months later, Buttermilk was completely socialized, albeit as the herd drill sergeant, who occasionally drove the others in mass gallops around the pasture.

Advance Preparations

You can almost bet that a newcomer is going to be put through a hazing period when entering an established group. But you can manage the situation to greatly reduce the hazards, starting with preliminary precautions even before the introductions take place. As for disease control, quarantining a new horse is the ideal approach, but it’s not practical in most horsekeeping situations. Effective quarantine requires that the new horse be stabled in a separate building at some distance from the resident horses and under the care of different handlers for several weeks. The following advance preparations will reduce both health and injury risks:

• Know your herd’s dynamics. Study the hierarchy and personality traits of your horses so that you can predict who will be the troublemakers and who will be the least aggressive. According to Houpt, much of the aggression displayed during the introduction will come from lower-rung horses looking to climb up the social ladder.
• Adjust your management routine to accommodate the newcomer. Shed-kept herds require roomy shelters if everyone is to fit in comfortably. If you feed your horses in the field, space the buckets or hay piles at least 20 feet apart. Allow the dominant horse to choose her feeding spot first.
• Pull hind shoes from aggressive horses and from the new horse until you are sure things have calmed down.
• Take a walking tour of the pasture to locate and take care of anything that might be trouble to running, flustered horses. Dead or low-hanging limbs, holes, protruding nails and splintered boards are obvious dangers. But keep in mind that although your acclimated horses known to give a wide berth to the disk harrow sitting in the pasture, for instance, a frightened newcomer might not be so careful.
• Block off any dead-end spaces and sheds in which horses might be trapped and terrorized, and plan an escape route for the new horse if you do need to remove him from a ruckus.

The Formal Introduction

Finally, after all your preparations, the new horse arrives. Presuming that the stranger is none the worse for his travels and that the environment and management routine has been “vetted” and corrected, it’s time to concentrate on minimizing aggression in the meeting of old and new.

• Turn the new guy out in an adjoining paddock for at least two or three days so that the horses can meet but still flee if threatened. However, the fence between the two paddocks needs to be sturdy and safe (no hoof-snaring wire, especially) or have a “hot” wire along the top to discourage contact by the horses on both sides of the fence.
• Move a middle-ranking, nonaggressive horse in with the newcomer so that the two can bond before the mass introduction.
• If possible, put the new horse in the pasture alone or with his new buddy so he can learn the lay of the land. Once familiarized, he’ll be less likely to run into danger trying to escape from aggression once the other horses are returned to the field.
• Make the big introduction during daylight, when the new horse can see well to run and you can be on hand for several hours to observe and step in if things get out of hand. Hold off if the footing is slick from mud or ice or the temperature is stressfully warm.
• Release the newcomer at least 15 to 20 minutes after feeding so there will be no food fights and most of the herd members are likely to be grazing or resting. They’ll be more relaxed then, and post-feeding running around shouldn’t cause a problem if the horses were fed lightly and if the other aspects of their daily routine (other than the new horse) have not been altered.
• The horses should call off the chase (at least temporarily) when they get tired or sweaty. If they don’t, a deeper-seated animosity is fueling the aggression and you may need to remove the new horse for the good of all.
• For a couple of weeks after the introduction, be particularly observant of all the herd members, checking for bites, bruises, lamenesses, sniffles, dull coats, lethargy and so forth, indicating illness or injury.

Throughout the fray that usually arises when an unfamiliar horse arrives upon the scene, remember that the uproar is an innate aspect of equine nature. Horses have been fighting and surviving these introductory battles for at least 10,000 years, usually without benefit of safety precautions taken by concerned managers.

That awareness may be cold comfort as you watch the whirl of horses trying to sort out their new roles and relationships, but keep in mind that horses’ aggressive behavior is intended only to threaten, not to maim or kill. In a matter of hours or days the group will most likely have settled into a sedate routine once again with the outsider now an accepted member of a smooth-functioning social order.

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