Social relationships in a herd of Sorraia horses Part II. Factors affecting affiliative relationships and sexual behaviours.

This research examines factors contributing to affiliative relationships and sexual behaviors in a herd of Sorraia horses, finding that kinship coefficient and dominance rank have the most impact. Despite the presence of affiliative relationships or higher relatedness, mares were not less aggressive towards each other. Moreover, the stallion showed a preference for less genetically related mares but was more sexually active with those that he was more genetically related to. This suggests that kinship might affect affiliative relationships among horses, though it does not necessarily imply that horses recognize kin.

Factors Affecting Affiliative Relationships

• The research analyzes the role of age, dominance rank, kinship, and aggressiveness in the relationships among a herd of Sorraia horses managed under extensive conditions. The subjects of this research were 10 adult mares aged between 5-18 years, who had known each other since birth, along with a stallion introduced for breeding purposes.
• The study findings indicated that kinship coefficient and dominance rank were key factors influencing affiliative relationships. Stronger bonds were found among mares with higher kinship, demonstrating that their relationships were reciprocal.
• Females spent more time with mares who were of close or lower-ranking order indicating the significance of the dominance hierarchy in these horses’ social relationships.

Influence of Aggressiveness and Kinship

• Interestingly, the study found that mares exhibiting stronger affiliative relationships or higher relatedness were not necessarily less aggressive towards each other, debunking any assumptions that close relationships could soften aggressive behaviors in these horses.
• The stallion exhibited complex relationship behavior as the affiliations formed with lower-ranking mares were stronger, however, he preferred proximal relationships with mares that were less genetically related to him.

Sexual Behavior and Kinship

• Furthermore, the stallion was found to engage in sexual behaviors more frequently with mares he was more genetically related to. This suggests that while kinship might matter in affiliative relationships, it was paradoxically of significance in the stallion’s sexual behaviors.
• The researchers noted that these results indicate that kinship might influence affiliative relationships among both familiar and unfamiliar horses. However, they stressed that these findings do not necessarily confirm that horses have a kin recognition system. Alternative explanations for these behaviours are also considered within the study.