We see a lot of polo saddles, and we see a lot of ill-fitting polo saddles. Some times the saddle being used is just not a good fit for a specific horse, but quite often, the saddle used to fit but doesn't any more.
Horses do change shape, with age, with fitness, or as the result of accidents or disease. But, a persistent issue is that many polo saddles themselves change shape. - they spread, i.e. they get wider at the shoulders (and lower at the withers). Generally, spreading is caused by the long term application of downward force on the head plate, or gullet plate, which reinforce the head of the saddle tree. In polo in particular, the downward force can be several times the player's weight, and this combined by the variation in force, is more than the head plates used by many polo saddle makers can withstand.
The problem of spreading is so pervasive in ;polo, that you would think that saddle makers had cottoned on to this and come up with appropriate solutions, but with a few exceptions, it is still not the case, and the cheaper the saddles get, the less likely it is that the issue will be addressed comprehensively.
The saddle on the left ( a well known brand) used to have the same shape as the MVP on the right, but has spread to the extent that it hits the 'withers' on our saddle stand. On a polo pony, this is obviously detrimental and is a surefire way of getting less from your horses than you would hope, and possibly injuring the pony.
Spreading may be detectable on some polo saddles within a few months, while it may take a year or two on others to spot the change. Whatever rate it happens at, it is usually too slow for us to perceive of it in in our daily use of the saddles. And we are not helped by the fact, that the saddle in question 'used to fit perfectly'.
It is not uncommon for older saddles to move from active playing service to use in practices and eventually to use for riding sets, which may exacerbate the problem of saddle spread. It could be argued that the horses being ridden in sets deserve the best fitting saddles in the barn as they spend more time under the saddle than any other horse.
The simplest way to keep a watchful eye on this issue (every few months) is to place your fingers of one hand between the pommel and the withers while riding and stick and balling (get up in the half and full seat as you would in a game). You will know immediately if you have a problematic saddle and pony combination and that it's time to find a better fitting saddle for your pony.
A key problem is that it's impossible to judge whether a given saddle will spread and by how much. So, if you are buying new polo saddles, demand a guarantee that the saddles will never spread. The MVP on the right in photo can be adjusted to fit different shapes and we guarantee that the saddle doesn't spread, ever!