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PostPosted: Thu Jan 21, 2016 12:45 pm 
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Joined: Wed May 27, 2015 10:20 am
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I am simply going by my experience of training and racing horses since the mid-1970s. I have seen many pony size racehorses that offered speed and profitability and soundness--not that there are those who don't, but many seem to out-perform the general consensus that size is better! I have also experienced a bias among my peers for the smallish racehorse in favor of the big tall ones.

I will quote from Dr. Robert Cook (who may still be a member of this group) from his book, SPECIFICATIONS OF SPEED IN THE RACEHORSE:

Quote:
1) "Even for the purpose of traction, power does not necessarily increase with size. For the purpose of speed, power probably decreases as weight increases. Speed requires a high power to weight ratio as exemplified by the cheetah and the deer. Large, heavy mammals are not, by nature fast. Large mammals also conserve body heat better than small ones. In the large horse this could lead to a problem and render it more likely to overheat than a small one. "

2) He says he thinks Tesio thought the average size of champions were around 15.3 hands while the average size of thoroughbreds were 16 hands.

3) He also says it is easier to recite famous horses that were smallish than large, i.e. Gimcrack (14 hands), Northern Dancer (15.1), Hyperion (15.1), Mill Reef (15.2), War Admiral (15.0), etc, etc.

4) He says when one searches for large horses over 16.2, it is difficult to find champions or certainly as many of as those below 16 hands.

5) "The reason large horses may not perform as well, on average, as small ones may have to do with the amount of oxygen they require to support strenuous exercise. A large horse, because of its greater body mass, requires a greater supply of oxygen to perform a given amount of work than a small horse. Yet, in spite of the this greater need, a large horse does not on the average have a larger airway than a small one."

6) There is another problem. Larger horses are more likely to show signs of a disease now known as recurrent laryngeal neurophathy (RLN).

7) Taking into account the greater likelihood of a large horse having a jaw that is too narrow for its size and adding to this the greater likelihood that such a horse will have an unfavorable ratio between supply and demand for air, a large horse (16.2 or over) is more likely to have a poor airway than a small horse.

8) . . .there is a purely mechanical reason to do with aerodynamics and physical laws governing the flow of gases along tubes. Resistance to gas flow increases sharply with any extension of the length of the tube. Large horses if they have long necks and long backs will have long airways than small compact horses because they would have to spend a larger proportion of heir available energy on the work of breathing. If your bellows are still handy, you can check this for yourself by extending the length of the bellows spout with a few inches of some rigid walled tubing. As smaller horses are better breathers and as better breathers are better striders, it follows that in general, small horses will be better performers.






An interesting perspective on human runners was written in the book THE SPORTS GENE which I feel can be applied to the racehorse as well:

Quote:
The Danes did a study on Kalenjin tribe athlete runners versus Danish boys. A greater portion of the body length of Kalenjin boys were composed of legs. The Kalenjin boys were on average two inches shorter than the Danish boys, but had legs that were about three quarters of an inch longer. The scientist most unique findings, though was not the length of the leg, but their girth. The volume and average thickness of the lower legs of the Kalenjin boys was 15-17% less than the Danish boys. The findings is substantial because the leg is akin to a pendulum, and the greater the weight at the end of the pendulum, the more energy is required to swinging it. Biologist have demonstrated this in human controlled conditions. In one particularly well controlled study, researchers experimented with adding weights onto different parts of the runners bodies, the waist, the upper thigh, the upper shin, and around the ankle. Even when the weight stayed the same, the farther down the leg it was placed the greater the energetic loss to the runners. In one phase, each runner had to wear 8 pounds around his waist which required about 4% more energy to run at a given pace compared with when he wasnt wearing 8 pounds of weight. But when the runners were subsequently equipped with 4 pound weight on each ankle they burned energy 24% more rapidly while running at the same pace even though their total weight had not changed one ounce from the previous condition. A separate research team calculated that adding just one tenth of one pound to the ankle increases oxygen consumption during running by 1%.

Proportionally, long legs and thin lower legs contribute separately to good running economy. Both within and between these groups of runners, lower leg thickness was an important predictor of running economy.


I just became an owner of a greyhound bitch and she is quite a fascinating animal to watch run and to study her conformation. Certainly with greyhounds, the previous Danish observations seems to be true, long linear legs are wonderful for speed! How does this translate to the equine? I am not sure. Certainly the short cannon has long been a hallmark of desirability, but I have not really seen much work to describe differences in leg length and muscularity to speed. Something to think about.

Lastly, the findings that distal weight on the runner is very important! This is why I use to religiously tie up my horses' tails in "mud tails" when they competed on an off track! A loose tail can really catch pounds of dirt in a race! It is also why I think running a horse in as short of hoof toe length is advantageous, less weight at the end and less cup to carry mud along with it, not to discount its economy of motion with a easier break-over.

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