Adaptive forgetting of place/object memory for dung in the domestic horse (Equus ferus caballus): Memory for a day.

Adaptive forgetting in domestic horses helps them remember the location and odor of dung deposits for about a day, assisting in risk assessment from other horses.

Research Purpose

• Investigate how domestic horses use memory related to the location (place) and odor (object) of dung deposits.
• Determine how long horses retain memory of specific dung encounters.
• Examine behavioral indicators such as approach frequency, sniff duration, nostril and ear use, and blinking during dung investigation.

Background

• Horses create “stud-piles” by depositing dung in specific locations, believed to communicate social or reproductive information.
• They engage in compulsive sniffing of dung, indicating it carries species-relevant cues.
• Studying memory related to these cues can reveal adaptation strategies in horses’ environmental and social behavior.

Methodology

• Subjects: Domestic horses (Equus ferus caballus).
• Settings: Experiments were conducted in 2 indoor and 4 outdoor riding arenas.
• Procedure:
  • Horses were led to either dung deposits or control objects at varying time intervals.
  • Each horse had opportunities to sniff these targets multiple times.
• Data collection: Video recordings were analyzed frame-by-frame focusing on:
  • Approach behavior.
  • Duration of sniffing.
  • Nostril preference or asymmetry during sniffing.
  • Ear position (to detect attention or laterality).
  • Blink frequency as horses stopped sniffing.

Key Findings

• Horses approached and sniffed dung deposits longer than non-dung objects, indicating strong interest in dung cues.
• During sniffing, horses moved their heads over the full surface of the dung deposit, exploring it thoroughly.
• There was no consistent nostril or ear preference while sniffing, suggesting bilateral sensory processing rather than lateralized sensing.
• Horses blinked when disengaging from sniffing, possibly indicating a cognitive or attentional shift.
• Memory insights:
  • Horses exhibited good memory for the dung and its location within the same day, as shown by reduced approaches and shorter sniffing on repeated encounters.
  • When tested across days, horses showed poor retention, approaching and sniffing dung similarly to first encounters, indicating loss or adaptive forgetting of that memory.

Interpretation and Significance

• The memory span for dung-related cues lasts roughly one day, which may be an adaptive mechanism.
• Forgetting dung cues after a day could prevent horses from over-relying on outdated information in dynamic social environments.
• This short-term memory enhances risk assessment by allowing horses to re-evaluate conspecific presence or social status without premature reactions based on old cues.
• Such adaptive forgetting could prevent unnecessary interruption of activities like foraging due to stale information about other horses.

Conclusion

• Domestic horses remember dung deposits and their locations within a day but tend to forget them after that period.
• This forgetfulness appears adaptive for optimizing social and environmental decision-making.
• Behavioral cues such as sniff duration and blinking provide important indicators of attention and cognitive processing in horses during olfactory investigation.