Dominance Behavior in Icelandic Horse Herds

 Many horse trainers claim that their training techniques mimic what happens in the horse herd.  Dominant, aggressive is justified because horses in the herd bite and kick each other so what the trainer does is mild in comparison with what the trainer does.  Interestingly research may or may not support their claims.  In the following study based on observations of a horse herd in the Netherlands, rank could be determined among the horses.  However amount of aggression displayed by individual horses did not correlated with rank.

Van Dierendonck, De Vries, and Schilder published a study on dominance behavior in Icelandic horses titled "An Analysis of Dominance, Its Behavioural Parameters and Possible Determinants in a Herd of Icelandic Horses in Captivity" (Netherlands Journal of Zoology, 1995).  In their review of previous research, they found a lack of clarity in how dominance is defined and hence how it impacted hierarchy among and between horses other than adult horses were almost always dominant over immature horses and horses newly introduced to the herd having lower rank.  The impact of weight, height, and age, and age at castration varied among studies .

Farm in Iceland--Cornell university

The researchers observed a herd of 26 Icelandic horses (6 geldings, 16 mares, 2 young stallions, and 2 young mares) and 5 ponies of different breeds at a farm in the Netherlands over a period of 6 months in 1984.  The horses were pastured year round with access to water, shelter, and food.  The non-Icelandic horses, young horses, and one mare with a probable hormonal disorder were excluded from the study. The horses had been together for several years.

Dominance behaviors were defined as offensive aggressive behaviors (attack, bite, threat to bite, approach with ears flattened,) versus avoidance.  Defensive aggressive behaviors were  kick, threat to kick, and buck.  Based on these observed behaviors the scientists could build a strictly linear relationship among the Icelandic geldings and mares.  The top five places in rank were taken by the older Icelandic mares with the sixth place held by a gelding with the rest of the rankings interspersed among mares and geldings.
Between sexes, certain lower ranking members could be dominant to higher ranking individuals.

• Age correlated with rank in the mixed sex herd ranking and among mares but not among the geldings.  
• Height did not correlate with rank when males and females were considered separately.  However height did correlate with the entire herd ranking with smaller horses ranking higher in this herd.
• Length of residency in the herd correlated higher with rank.
• Rank position surprisingly did not correlate well with amount of aggression displayed.
• Submission correlated with rank.
• Age at castration  linked with sexual experience  correlated with rank.  In other words, the amount of sexual experience and the opportunity to develop and practice male displays rather than age of castration per se influenced ranking among geldings.
• Mares with foals temporarily can gain in herd ranking.
• Ranking of adult mares correlated positively with their adult offspring.
• If a mare exhibited more aggressive behavior, her offspring was likely to be observed exhibiting more frequent aggressive behavior (which could be due to heredity and/or learned behavior).

This study did not observe and correlation between rank and allogrooming, kinship, and social bonds.  However pairs of horses closer in rank tended to spend more time close to each other.

Source: http://web.science.uu.nl/behaviour/deVries/VanDierendonck1995.pdf