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Overwhelmed
Neither for or against but history, when lives depended on sound horses, did have several experiments, from the book Small Horses In Warfare http://www.lrgaf.org/small-horses.htm
Ponies in India.
Captain L. E. Nolan, in Cavalry History and Tactics (1860), gives an account of an experimental march made by 200 of the 15th Hussars from Bangalore to Hyderabad and back, 800 miles. The objects of the march were to test the capabilities of the troop horses and to ascertain if there were anything to choose between stallions and geldings in respect of endurance. To arrive at a solution of the latter question, one hundred of the men were mounted on entires and the other hundred on horses which had been castrated only six months previously, regardless of age, for the purpose of making the experiment.
The squadrons marched to their destination, took part in field-days and pageants, and started to reach Bangalore by forced marches; they accomplished the last 180 miles at a rate of thirty miles per day, bringing in only one led horse, the remainder being perfectly sound and fit for further work. One horse, a 14.3 Persian, carried a corporal who, with his accoutrements, rode 22 stone 7 lbs. It may be added that there was nothing to choose between the performances of the stallions and geldings; though the fact that the latter had so recently been castrated was held to make their achievement the more creditable.
A forced march such as this has far more value as testimony to staying power than a more trying feat performed by a single animal; but mention must be made of Captain Horne's ride. This officer, who belonged to the Madras Horse Artillery, undertook in 1841 to ride his grey Arab, "Jumping Jimmy," 400 miles in five days on the Bangalore race-course; and accomplished his task with three hours and five minutes to spare, the horse doing the last 79 miles 5 furlongs in 19 hours 55 minutes, and being quite ready for his corn when pulled up. General Tweedie, in his work on The Arabian Horse (1894), quotes the above particulars from the Bengal Sporting Magazine, in whose pages full details are given.
How long did they live?
Forty years ago a horse of eleven was worth a lot less money than one of nine.