American Quarter Horses are renowned for their speed, agility, and calm disposition. Consequently over four million Quarter Horses are used as working horses on ranches, as show horses or at rodeos. New research used ‘next-generation’ sequencing to map variation in the genome of a Quarter Horse mare. Analysis of genetic variants associated with specific traits showed that compared to a thoroughbred the Quarter Horse’s genome was enriched for variants in genes involved in sensory perception, signal transduction and the immune system.