It seems that the refinement of the racehorse through selective breeding has reached a ceiling because they are not getting any quicker. In fact, many of today’s records are 50 years old. For example, the great Classic race, the Derby, was run in record time in 1926. The horse, Coronach, who set the record managed 38 mph over the 1.5-mile course. There may be people other than Dr. Desmond Morris (who provided that information) who think that the course record for the Derby is by another horse. However, the point is that there has been little improvement, certainly in comparison to humans.
There have been great advances in the times set by human world record holders and Olympic champions over the century. The improvements by racing horses are far less impressive.
Dr. Morris states that there are two possible reasons:
- The original gene pool of the foundation horses is too narrow. It is too restricted because of the small number of initial founding stock. I discuss this further below.
- A second reason is that the training techniques of recent and modern top racehorse trainers is deficient in some way.
Royal patronage in the 18th-century in the UK injected a burst of activity into the horse racing scene. Serious horse racing began. The Middle East provided three founding and magnificent Arab stallions. They were imported and bred with about 50 mares to start a new breeding line called thoroughbred.
In 1793 the General Stud Book was created. This recorded the pedigree of each thoroughbred racehorse. It is believed that the idea for the General Stud Book came from Arab horse breeders who had been selectively breeding for many years and who kept records of the lineage of each of their champion horses. The word “thoroughbred” is a literal translation of the Arab word ‘Kehilan’ which is a reference to a horse that has been “pure-bred all through”.
Crucially, not long after it was started the Stud Book was closed preventing any new founding stock to be entered into it. Accordingly, over the next 200 years of thoroughbred horse breeding the entire stock was based upon a very tight or narrow genetic pool.
In fact, it is estimated that 81% of the genetic make-up of all modern thoroughbred racehorses is based upon just 31 original horses according to Dr. Morris in his book HORSEWATCHING.
There was some initial improvement as demonstrated by improvements almost annually over the hundred years after the beginning of the Stud Book. There was an improvement of about 2% per year until about 1900.
And during the 19th century the horses became larger at about 1 inch every 25 years. Their legs became longer and rangier. And that was that, as they say. It seems that the limit for improvement has been reached because of the small gene pool of the foundation horses.
In the cat fancy world, if you want to improve a purebred cat in terms of health while perhaps destroying the appearance as per the breed standard, you inject into that breeding line entirely fresh genes from perhaps a moggy or another breed. This helps to eliminate a compromised immune system due to inbreeding depression.
In conclusion, therefore, racehorse breeders need to inject fresh genes into their breeding stock and breeding lines and/or trainers need to review what they’re doing and bring their training up to scratch in the modern world if fresh records are to be set.