Most horses, with the proper training, can learn to play polo.
Building A String Of Polo Ponies
Polo ponies are like polo players:
One of the most important things to look for is a good temperament in a horse. If you select a polo pony that you cannot play safely, you will be in trouble from the start.
Most beginners imagine their perfect polo pony as a beautiful chestnut mare, only to find out later that it was not the right one for their level of ability. It's much better to select a quiet, easy horse that is at least 8 to 10 years old with no bad habits. A horse is not old at 10 years, but actually in the prime of life.
Each polo pony in your string will require housing, feed, watering, exercise, grooming, veterinary care, and training.
Stalls
A stall for a polo pony should be 10 ft square with a dry, soft bed of shavings.
Exercise
A polo pony must be exercised daily. When turned out to pasture a polo pony will regulate its own exercise. When playing polo, each horse must be ridden or jogged for at least thirty minutes once or twice each day.
Grooming
A polo pony must be groomed daily. A rubber comb should be used to massage the skin and loosen dead hair and dirt. Each foot should be picked up, cleaned, and examined daily.
Introducing a Horse to Polo
It takes a great deal of time turn a horse into a "made pony" that loves to play the equestrian sport of polo. A horse must be well trained for riding before introducing it to polo. A horse should neck rein with minimal pressure, work well off of leg cues, hold a gait without breaking, bucking, kicking, or shying, and be able to work around other horses. A horse must also be slowly and gently introduced to polo equipment. The horse is desensitized to the mallet by letting him see it and smell it first. Next, a mallet is gently rubbed against the horse's body. Eventually, a polo trainer will swing a mallet around and under the horse while riding. The same approach is used to get a horse familiar with a polo ball.
Suggested Reading
To learn more about training polo ponies read the classic text on the subject "Modern Polo" by Captain E.D. Miller, Edited by M. Horace Hayes, 1898, 1902.