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Owners consider equine companionship an important part of horse welfare, but are they paying enough attention to the composition of the groups?
A study published this week in the journal Animals explores how the make-up of groups affects the welfare of horses kept at pasture, finding that certain combinations create higher aggression levels.
“By nature, horses are highly social animals, depending on the group for survival,” University of Iceland researchers Hrefna Sigurjónsdóttir and Hans Haraldsson said.
The social nature of horses meant they needed plenty of opportunities to interact to form bonds and learn from their elders, they said.
“Social bonds are likely to play an important role for social cohesion in group-living domestic horses.”
Therefore, management practices that minimized aggression and gave the horses ample opportunities to socially and emotionally bond are to be recommended.
The two researchers focused their study on 426 Icelandic horses in 20 groups of at least eight horses each.
The data they used came from earlier independent studies carried out over a period spanning 15 years.
The pair looked at group size, density of horses in the pasture, sex ratio, the proportion of adults, the numbers of young foals present, the number of friends, group stability and the presence of stallions.
They also looked at the effect of the season and whether hay was provided.
They found that aggression was lowest where the group composition was like the natural system found in the wild – that is, with a stallion, mares and their young foals.
In groups without a stallion, horses appeared to be better behaved when foals were present, with low levels of aggression found.
The pair reported that stability in a group was clearly important, as this also seemed to encourage less aggressive behaviour.
“The highest aggression was found in groups of unfamiliar yearlings,” Sigurjónsdóttir and Hans Haraldsson wrote.
More socially driven grooming was noted in groups with a higher ratio of young horses, which suggested they were forming bonds. Later, they groomed less, but had developed a preference for certain individuals.
“Horse owners should all be aware of the importance of planning the composition of horse groups and to keep the membership as stable as possible in order to ensure good welfare,” they said.
They found that high social activity was mostly limited to a few individuals, while the majority of horses interacted at lower levels.
Aggressive encounters were more frequent in male horses while the frequency of socially driven grooming was found to be similar between the sexes.
There was little difference in median aggression among age groups except for the oldest horses, who were more aggressive than younger horses.
“Interestingly, the frequency of submission is also high among the oldest horses. It appears that while they strive to keep their status by elevating aggression they run a higher risk of eliciting aggression of high-ranking individuals, causing them to submit.”
Aggression levels clearly varied with season, being the lowest in spring and the highest in winter. Grooming frequencies were similar in all seasons.
Provision of hay seemed to increase aggressive behaviour.
The strongest factors that influenced aggression were the number of foals present in the groups and stability.
The proportion of males in the groups was linked with aggression and submission across the 20 groups. However, this was not found to be true for the groups without a stallion.
They said the individual frequencies of aggressive interactions in the groups of Icelandic horses used in the study were generally low.
“In non-stallion groups, stability of group membership has a strong overall correlation with less aggression.
“In stable groups, horses are more knowledgeable about the social network and hence there is less need for the dominant horses to give strong aggressive signals.”
The arrival of newcomers was linked with an increase in social interactions, most of all aggressive threats. “Prior studies have shown that there is a rapid decrease in these interactions if the membership remains unchanged.”
They concluded: “This study emphasizes the need for horse caretakers to consider group stability and group composition in domestic horse management.
“Group composition which is similar to the natural social system with both sexes (sub-adults and foals) and stable membership of adult horses is likely to provide the best social environment for all horses because of very low aggression levels.
“Also, it is likely to offer the best conditions for young horses to learn social skills, because of the presence of older and experienced horses and the possibilities to associate with peers.
“Such groups, or groups where stallions are replaced by adult geldings, could easily be taken up as a management practice. Peer groups should be avoided, especially if composed of young unfamiliar horses, because of high levels of aggression.”
Sigurjónsdóttir and Haraldsson said the importance of the welfare of horses can never be overemphasized.
“Recent research on the cognitive abilities of horses and their emotions has shown that horses are more complex in these areas than previously thought. It is our belief that awareness of such findings will affect both personal views and legislation on horse welfare in the near future.”
Significance of Group Composition for the Welfare of Pastured Horses
Hrefna Sigurjónsdóttir and Hans Haraldsson.
Animals 2019, 9(1), 14; doi: 10.3390/ani9010014