The question of why some race horses are natural sprinters and others are born stayers has finally been answered, it seems.

Research by scientists at Trinity College Dublin and University College Dublin have unravelled the workings of the "speed gene" in thoroughbred racers.

This is the genetic code that determines muscular-skeletal growth, which in turn translates, they say, into an ability to run for longer.

The discovery could prove hugely valuable for racehorse breeders and trainers, when it comes to determining the optimum distance for a given thoroughbred.

"Our data provides the first mechanistic evidence as to the specific element of the 'speed gene' that acts as the sole protagonist in dictating its expression in the thoroughbred," said Richard Porter, Associate Professor in Biochemistry at Trinity College Dublin and senior author of the study.

"As a result, this element is the key genetic factor in determining distance aptitude in thoroughbred horses."

A range of environmental factors, including training regime, are known to influence a thoroughbred's abilities to run either fast or long.

But genetic factors also have a huge influence, research has shown.

Past work by UCD Professor Emmeline Hill had demonstrated that different versions of the myostatin gene were almost solely responsible for the fundamental genetic based ability of racehorses ability to run distances.

That is because myostatin is responsible for regulating bone and muscle growth.

The discovery of this "speed gene" led to horses being classified as either sprinters because they have a "CC" copy, middle distance runners because they had a "CT" copy or long distance as they had a "TT" version.

What is going on inside those genes and why they impact on performance has remained a mystery though.

This research, published in PLOS One, has pinpointed the non-coding section of the "speed gene" that is responsible for limiting the production of myostatin protein.

This in turn, the scientists say, affects skeletal muscle development and their ability to run longer race distances.

If the data can be used to assess the genetic basis of each thoroughbred, the findings could prove a "winner alright" for the multi-billion euro breeding industry.