Olfactory Stimulation as Environmental Enrichment for Domestic Horses—A Review

SIMPLE SUMMARY: Equine welfare is a topic that has attracted the attention of both the scientific community and the public. In the domestic environment, horses are often kept in suboptimal conditions that limit the expression of species-typical behaviors and compromise their welfare. Environmental enrichment strategies have been identified as an interesting option to make the domestic environment more interactive and complex, resulting in an improvement in the animal’s quality of life. Olfactory stimulation, a form of sensory environmental enrichment that aims to trigger the sense of smell through the introduction of odors, has shown promise for horses. This review aims to present current information on equine olfaction, demonstrating its relevance as a sensory modality and exploring the potential that olfactory stimulation has as environmental enrichment for the species. ABSTRACT: Horses constantly face several challenges inherent to the domestic environment, and it is common for the expression of their natural behavior to be drastically limited. Environmental enrichment has been suggested as an alternative to improve the captive situation of domestic horses. Among the recently proposed enrichment strategies, olfactory stimulation has emerged as a method for improving several aspects related to animal behavior. Olfaction is a sensory modality that plays a significant role in the expression of equine behavior, and in recent years, studies have shown that olfactory stimulation can influence the physiological and behavioral parameters of horses. This review provides current information on the anatomical particularities of the equine olfactory system, presents the physiological mechanisms involved in the odor detection process, and demonstrates how stress can interfere with this process. Finally, the use of olfactory stimulation as an environmental enrichment for domestic horses (Equus ferus caballus) is explored. The need for new studies that answer pertinent questions related to this topic is discussed throughout the manuscript.