Can stallions get along better than we think?

New research suggests that, if some precautions are taken, it may be possible to safely keep stallions together.
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A new Swiss study challenges conventional notions about how stallions are best housed and managed. 

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Researchers at the Swiss National Stud Farm in Avenches designed an experiment to determine whether domesticated stallions could live together peacefully, as do males in the wild. 

"In the wild, stallions start forming bachelor bands from the age of 2 1/2 and stay together until the age of 4 or 5, when they acquire their owns harems," says Sabrina Briefer Freymond. "These bachelor bands allow stallions to improve skills necessary to acquire and maintain a harem and to develop their physical stamina. Old stallions that have lost their harem can also be found in bachelor bands."

In contrast, domesticated stallions are often segregated from other horses at an early age and are kept in isolation for the remainder of their lives to minimize fighting and prevent injury. But, says Briefer Freymond, this "safety" comes at a cost to the stallion's mental health because he is denied social interaction with other animals. 

For their initial study the Swiss researchers gradually merged five stallions into one herd. For the first 14 days, they were kept in individual stalls separated by partitions with rail tops, which allowed them to hear, see, smell and partially touch each other. They were then moved together to a single outdoor pasture. During the first three weeks, the stallions were observed or videotaped nearly continually, and their social interactions were documented during the day. Specifically, researchers looked for three types of interactions:

agonistic--any contact or interaction that resulted in increased distance between the two animals (e.g., chasing or kicking)

ritual/investigative--any non-contact interactions used to assess each other's social station without fighting (e.g., sniffing manure)

affiliative--interactions that were neither agonistic nor ritual (e.g., grooming each other or playing). 

The researchers also measured the stability of the herd hierarchy by ranking each horse's dominance one month, two months and three months after the herd was formed. 

The researchers repeated the experiment a year later with a group of eight new stallions. The study horses were 8 to 19 years old and had lived at the National Stud for at least five years. They were used for breeding and driving, and all but one had been hitched next to another stallion for work at some time. 

Looking at all the data, the researchers found the first three days were, as expected, somewhat volatile, but agonistic and ritualistic behaviors decreased dramatically thereafter. Eventually, these behaviors decreased to levels seen in wild bachelor bands. Herd hierarchy was considered stable after three months during the first trial and after two months in the second trial. 

"In comparison to a group of mares, conflicts between stallions are much more impressive because stallions use displays and rituals aimed at showing off their fighting abilities," says Briefer Freymond, adding that with just a few precautions, injuries were kept to a minimum. "To avoid stallions getting seriously hurt, it is important to remove horseshoes before the integration and to keep the stallion group far away from mares, in order to avoid conflicts between them. We observed some wounds due to kicks and bites, but none of the stallions had to be removed from the group because of injuries caused by social interactions. 

The fact that the stallions were introduced to each other slowly also contributed to the smooth transition, says Briefer Freymond: "It has been shown in other studies that pre-exposing unfamiliar horses by placing them in adjacent stables reduces both aggressive and nonaggressive interactions when they physically meet for the first time. This could be due to an exchange of visual and olfactory information about fighting abilities between horses through adjacent stables, which could allow them to establish dominance relationships before being integrated in a group. Our study shows that integrating horses that are experienced in group housing (i.e., have already been in groups before) also decreases the frequency of interactions and thus the potential risk of injuries." 

The researchers conclude that a housing system that keeps stallions together is not only feasible but could potentially improve the welfare of the horses while reducing the workload of the caretakers. 

Reference: "Pattern of social interactions after group integration: A possibility to keep stallions in a group," PLoS ONE, January 2013.