Pushball on horseback: small research

Dear pushball lovers,

For this moment I am interested in the history of "pushball on horseback" and its origine. Do you play pushball in compatition in your country? Are you organised? What kind of rules do you use? Which tactics work (not)?
Can elephant play pushball with a large pushball (like the horses) or only with a big football with their nose? See YouTube.com site.

My background:
I'm Dutch and live in Rotterdam (Main Port of Europe). My first experience (with my horse) with pushball was in 1982 in Offental, Germany. Now we are training pony's and horses in Rotterdam, The Netherlands. After 3 year searching I finally found a large pushball for the horses. It's difficult to find the right ball-size for each horse breed - for the safety of the game is this essential! The pushball may not get stuck under the belly of the horse/pony.
This year I found Pushball Rules from 1928, used in Germany (origine Italy).