The quarter horse, or American quarter horse, is one of the most popular breeds from North America. It was named after its exceptional speed on tracks distancing a quarter mile or less.
When Spanish conquistadors discovered the American continents and started to colonise the land, they needed horses for battle, moving heavy loads and conquering ground. As America had no native horses, the conquistadors imported their own, many of which were of Iberian breeding, from Europe. Over the centuries, the descendants of these horses and others that were imported since adapted to the new land and became the foundation stock for many American breeds like the mustang, walking horses, paints and quarter horses.
Due to its mixed heritage, nearly all colours are present in the breed. The base colours are the most abundant, followed by the cream and dun dilutions. Champagne and pearl are quite rare, and silver is known only in very few families.
Where a mixed history resulted in a wide range of colours, the same could be said for white patterns. However, white patterns and their spreading were very much restricted, as white on the horse's bodies or painted horses were undesired. As such, horses with white too much white, or producing such foals, were excluded from registering with the studbook, removing them from the gene pool. Many of these would eventually be registered with the paint horse registry, where white patterns were welcomed. But as the quarter horse registry continued to allow small amounts of white that fell within the common markings category, white patterns could survive as long as they remained within the designated borders. By breeding for a selective range of white and removing animals with the unwanted phenotype from the breeding pool, only white patterns that could mimic normal or accepted white markings managed to pertain. Occasionally, their offspring could still inherit more than one copy of the pattern or their boosters, resulting in the so-called 'crop-outs'.
Recently, in ... the American Quarter Horse Registry decided to allow these crop-outs within the population.