Reiter und Pferd erhalten zusammen eine Startnummer, mit der sie sich für Prüfungen anmelden können.

I've been looking for a translation for 'Startnummer' for quite some time now, but keep failing irrespective of the dictionary I look in. Is this a concept that's not being used in English, or am I simply too stupid to figure it out?

Any help is greatly appreciated. A merry Xmas to everyone on the forum.