Lateralized suckling in domestic horses (Equus caballus).

This research paper investigated if young horses (foals) demonstrate a brain lateralization effect when suckling, potentially indicating a preferred processing of stimuli in one cerebral hemisphere. The study found no general trend, but noted significant individual variations in preferred suckling side, which increased with age and are thought to reflect motor lateralization.

Introduction to Brain Lateralization in Horses

• The basis of the research is the concept of brain lateralization, where one side of the brain may be more dominant in the processing of certain stimuli, leading to more effective usage of that input.
• In horses, this takes the form of both motor and sensory lateralization patterns.
• Motor lateralization is identifiable when a horse predominantly uses one side, either left or right, for specific actions.
• Sensory lateralization refers to a preference to process sensory information on a particular side of the brain, such as a visual lateralized response.

Research Aim and Method

• The study’s aim was to investigate whether there was a lateralized response in foals during suckling, a naturally side-biased behavior.
• The researchers hypothesized that the foals’ preferred suckling side could be a result of either a motor or visual lateralization.
• Visual lateralization would be demonstrated if the foals had a tendency to suckle from their mother’s right side, therefore potentially allowing for better detection of danger with their left eye (connected to the right hemisphere).
• The sample size of the study was 79 foals, and the researchers took note of the side each foal preferred to suckle from.

Findings and Interpretation

• The researchers did not find a population-wide trend indicating a preferred suckling side.
• However, they did find significant differences among individual foals. Approximately 35.4% of the foals demonstrated a strong preference for suckling from either the right or left side, and this preference grew stronger as the animals aged.
• The mother horses did not appear to influence the suckling side preference of the foals, either through side-biased rejection or termination of suckling.
• The researchers concluded that a general pattern of suckling while keeping the left eye open (for better danger detection and recognition) seemed unlikely for foals up to 7 months old.
• At this age, foals are probably either too young or fully focused on suckling, and therefore rely on their mothers’ vigilance for protection instead.
• The researchers suggest the individual side preferences displayed amongst foals are likely based on motor lateralization, not sensory.