Keeping horses in social groups is considered an important element of welfare, but not all equines necessarily get along.
It is important to consider friendship when managing group compositions, according to researchers.
“As in many mammals, horses form long-lasting social relationships with group members, so-called social bonds,” Riccarda Wolter, Volker Stefanski and Konstanze Krueger write in the open-access journal Animals.
“Horses prefer to affiliate with a small subset of the available group members. The best method of measuring social bonds in horses is still not clearly defined and it can be performed in many different ways.”
The German researchers noted that measuring the type, frequency, and duration of friendly social behaviour can be useful in assessing these friendships.
In many species, it is common to use the frequency of mutual grooming. However, because mutual grooming behaviour is comparatively rare in horses, it does not allow for a robust analysis.
For example, some feral horses groom mutually at least once an hour, while others in the group may only participate once every ten hours, and some do not groom at all.
The trio set out in their study to explore the most reliable parameter, or combination of parameters, for the analysis of social bonds in a species that seldom grooms, such as the horse.
They observed social behaviours and the time they spent in close proximity across a total of 145 horses, all living under semi-wild conditions. Thirty-six of them were Przewalski’s horses, kept in five groups, and 109 were feral horses, kept in six groups.
Each group was monitored for 15 hours across three days within one week, which they said was long enough to provide robust and reliable data.
The study team compared the frequencies of mutual grooming, friendly approaches, and close proximity, in pairs of horses. They found that all three were robust parameters for measuring social bonds.
“Social relationships appeared to be stronger in smaller rather than in larger groups, as has been claimed for social groups in general,” they reported.
“In the present study, this is demonstrated by the high frequency of friendly approaches and the horses’ staying in close proximity in small groups.”
The fact that grooming was more frequent in larger groups, with more potential instability, may indicate the appeasing, aggression-regulating, pro-social value of mutual grooming, they said.
“A follow-up study is needed to investigate whether, in addition to friendly approaches, further proactive behaviour, such as grazing and resting together, could be combined with the mutual grooming data to analyze social bonds in horses even more quickly and precisely.”
Further individual factors, such as reproductive status and age, which were missing for most of the observed horses in the present study, may also be considered.
“Other behaviors not found to be integral to this short-term study may also be important when assessing social bonds or the development of social bonds in social species, but may require longer observation periods.”
They concluded that observation of proactive behaviour, such as mutual grooming and friendly approaches, or of spatial proximity between group members, were suitable for social bond analysis in horses within a short time frame of 15 hours.
“We expect a combination of friendly approaches and mutual grooming, or the measurement of spatial proximity, to be robust for the majority of horse groups, as this was the case for all the groups in the present study, even though the groups varied in their composition and the parameters of the individual animals.”
Wolter and Krueger are both with the University of Regensburg and Nürtingen-Geislingen University; Stefanski is with the University of Hohenheim.
Parameters for the Analysis of Social Bonds in Horses
Riccarda Wolter, Volker Stefanski and Konstanze Krueger
Animals 2018, 8(11), 191; doi:10.3390/ani8110191