When breeding horses using biomechanics as a tool for analysis, the underlying premise is that one should try to match the horses who are most similar. The reason for this approach is that if breeders mate very similar (biomechanical) types, the range of variation should be smaller and therefore, there should be more good prospects from the matings.
Obviously, breeders also would be trying to mate the best stock they possess, but the approach from biomechanical analysis is a modest tweak on the concept of breeding the best to the best.
Some of the best, especially the super horses of the breed, are highly individual, and some of them are nearly biomechanically unique in how their parts work together to make them so talented.
Not surprisingly, many of the most gifted racehorses possess outstanding physical and mechanical qualities. They are frequently almost off the charts for some of the special qualities they possess.
Having a special gift is a great blessing to that individual and to those lucky enough to be associated with that horse. But many horsemen will immediately note that some of the greatest racehorses have difficulty “reproducing themselves” as sires and dams.
And in general, the reason for this is that the stallion or mare is so specialized, even to the point of being a virtually perfect specimen in many regards, that the changes required to breed another generation produce offspring less perfect than the sire or dam.
Stallions and mares who are biomechanically quite specialized are identified as outliers from the “norm of the breed.” The norms of the breed are very important because the great or considerably talented racehorses who fit those norms have much higher opportunities of becoming successful breeding stock.
The reason is that any mating is likely to produce a regression toward the norm of the breed. And if a high-class stallion or mare is already at or near the norm, its offspring should have less variation from the parents’ good qualities.
The poster boys for breeding toward the norm are Mr. Prospector and Secretariat. Members of the glorious crop of 1970 – which also included Allez France, Dahlia, Forego, Desert Vixen, Sham, Stop the Music, Royal Glint, and Ancient Title – Mr. Prospector and Secretariat had a reversal of rank in their importance as racehorses and stallions.
Whereas Secretariat was the king of the world on the racetrack, Mr. Prospector was a vastly talented but only good stakes winner during his time on the track.
Once they went to stud, however, things changed. Secretariat was a good stallion, but Mr. Prospector became the leading sire and the important sire of sires.
In terms of their biomechanics, this isn’t a surprise. Secretariat was a highly specialized individual and nearly perfect specimen of a racehorse.
Secretariat had an extraordinary stride, not just in its length but in his capacity to keep rolling on with that big stride furlong after furlong.
In combination with his stride, Secretariat also possessed relatively little early speed. It wasn’t an accident that he raced from behind, especially when he was sprinting at 2. Despite his massive muscling, Secretariat did not have the gate speed to compete with sprinters early, but once he got into his stride, he could open the jets and leave his opponents in the dust.
Those qualities made Secretariat very special, but few racehorses had the same qualities, and when trying to match him with mares, the results frequently were not what breeders hoped for.
In Mr. Prospector, however, breeders found a talented racehorse who was not unique but was so well-positioned in regard to the norms of the breed that he was able to pass on his many good qualities with relatively little alteration.
Northern Dancer was also an example of this type of horse suited to mix well with many sorts of mares, and the most popular and successful cross or “nick” has been the Northern Dancer – Mr. Prospector cross.
As the two predominant sires of the past 30 years, it seems logical that they would mix well. They were also quite similar in biomechanical traits (not the same thing as looking exactly alike), and they were both near the norm at the center of the breed.