Interesting question LG!
I am certainly of the opinion that a mare will never develop into a good strider unless she is trained to be a good strider. Most trainers do not go to the trouble of extra training, to improve stride. Basically most trainers will keep a horse healthy, fit and try to improve distance or speed. However, usually stride is something that most trainers don't have the know how to improve. It takes a tremendous amount of work to improve stride, and a good natural strider is always preferable.

A mare can improve out of sight depending on what's been holding her back.
Mares are notoriously moody and can get out of sorts for many reasons.
When a mare puts it all together on the day, she can improve dramatically.

If I give the example of mares that run favourite by age, this might shed some light:

All Mares Favourite
29.80% S/R

4yo Mares Favourite
30.31% S/R

5yo Mares Favourite
28.85% S/R

6yo Mares Favourite
28.09% S/R

7yo Mares Favourite
26.15% S/R

>7yo Mares Favourite
28.30% S/R

I'd say it depends on the mare, but overall they do tend to train off with age, it also depends on what age they started their race career.

As it stands, with current training methods and the cost of time, it is highly unlikely that a mare will increase it's stride length, unless she has had an injury stopping her stride out.

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