Working memory is vital for complex tasks but is under-explored in non-human species, such as horses. This study evaluates horse working memory through an invisible displacement task involving delayed choices. Twenty-six horses were tasked with selecting between two buckets containing a treat, with delay intervals of 10, 30, or 45 seconds between presentation and decision-making. The accuracy of correct choices was influenced by delay duration, presence of distracting stimuli, and performance in basic condition. Results showed that horses could retain information for up to 30 seconds and process information about object displacement. These findings enhance our understanding of horse cognition, revealing their capacity for simple reasoning and a longer working memory span than previously acknowledged.