Abstract: Earlier research indicates that stallions might either prevent social interactions between mares in their
herds directly or indirectly by their presence (Feist and McCullough, 1976; Sigurjonsdottir et al.,
2003) The impact of stallions on the social interactions between harem members was studied in 6
groups of Icelandic horses in 2004, 2006 and 2007 for altogether 525 hours. Four of the groups were
permanently living together under semi-feral conditions, while two were temporary breeding groups. In
addition, temporary and permanent groups were compared and the effect of the stability of the group
on the social behaviour of horses was investigated .
The results show that stallions seldom intervene directly in social interactions between harem
members. However, the hierarchies were less rigid and fewer friendship bonds were found in the
groups compared to what has been found in groups without stallions in Iceland. These results give
some support to our prediction that the stallion does indirectly suppress social interactions of herd
members.
The stability of the group was found to affect the aggression rate, since a higher aggression rate was
found in the temporary groups compared to the permanent groups. The number of preferred
allogrooming partners of the horses was also affected to some extent, as a significantly lower number
of allogrooming partners was found in the most unstable group compared to all the other groups. The
results have significance for further research in the field of social structure of mammals, and may also
be applied in the management of horses and other domestic animals.