Science  /  Comparison

A Gallop Through a Horse's Pedigree

An in-depth look at horse breeding.

Not only was The Gray Ghost a great runner, but he was a great progenitor as well. Three of his progeny, Northern Dancer, Kauai King, and Majestic Prince all won two of the three Triple Crown races in their careers. Native Dancer’s grandson, Mr. Prospector, was a tremendous progenitor too and fathered more than a thousand named colts. So desired were Prospector’s genetics that by 2018, every entrant in the Kentucky Derby had some biological connection to him and hence to Native Dancer.

But thoroughbreds are notoriously inbred. Every thoroughbred alive today is an offspring of just three stallions: Darley Arabian, Godolphin Arabian, and Byerley Turk, and a select number of mares dating back to 17th and 18th century England. Darley Arabian and Godolphin Arabian were both said to have come from Yemen. The origins of Byerly Turk are less known although he was captured in the Battle of Buda in Hungary.

In a study published by Scientific Reports of more than 10,000 thoroughbreds over a 50-year period, geneticists discovered that the Thoroughbreds are becoming still more inbred due to the high pressure and money involved in producing winning horses. The scientists looked for homozygosity and identical alleles among the 10,000 horses and noticed that in particular, the last fifteen years have seen increases in those genetic traits.

Registered Quarter Horses have much more genetic diversity, or haplotype richness as geneticists put it, than thoroughbreds. The quarter-horse breed has only been official since 1940, although the aim to breed a quarter-horse-type animal has been going on since the colonial era. And today there are more than six million registered quarter horses, making it the most popular horse breed.

The Quarter Horse lineage comes from English stock horses bred with Chickasaw horses in the American colonial era. Then a thoroughbred descendant of Godolphin was introduced to the breed. Finally, blood from western mustangs was introduced. But it may have been the original breeding of the Chickasaw Indians with horses captured from the Spanish conquistadors that created the foundation of the American Quarter Horse. The Chickasaw loved to race their horses on short straight courses and the American settlers soon picked up on the sport. The Chickasaw horses with their stocky build were the fastest over those short courses and in high demand.