The relationship of dominance, reproductive state and stress in female horses (Equus caballus).

The abstract discusses research conducted on the impact of dominance and reproductive state on stress levels in domestic horses, particularly female ones. It further outlines the implications of these factors in influencing the activity behaviours and glucocorticoid levels of these animals.

Overview of the Project

• The primary objective of the study was to investigate how dominance rank and reproductive state could affect stress levels in domestic horses, a non-cooperative breeding and herbivorous species.
• The study aimed to fill the gap in previous research that hadn’t directly examined the effect of reproductive state on dominance and stress among animals.

The Research Process

• The researchers observed the social interactions of female horses in a pasture setting. These horses were either lactating or non-lactating.
• They also measured the levels of faecal glucocorticoids, which are the metabolized by-products of the stress hormone cortisol.

Findings from the Study

• The study revealed that the stress hormone levels or faecal glucocorticoid metabolite levels did not vary significantly between the horses’ reproductive states or between their dominance ranks.
• However, the researchers observed notable differences in the horses’ activities depending on whether they were lactating or not.
• Horses in the lactating state spent significantly more time eating and noticeably less time being alert or socializing, suggesting the increased energy demands of lactation.

Implications of the Findings

• The findings imply that as non-cooperative breeders, the social nature of horses does not constrain their reproduction or resource acquisition based on their dominance rank.
• This contrasts with the dominant-stress hypothesis and subordinate-stress hypothesis, both of which maintain that higher-ranking animals exhibit lower stress levels since they can secure more resources or win more conflicts.
• The research supports instead, a rank-independent stress hypothesis, suggesting that stress levels among horses are not determined by their social or reproductive rankings.