Question about buying an affiliated horse...

[JOJOBA]

Im not doing, but may do one day!
I was just wondering this as I looked through ads the other day.
If you buy a horse which has, say *random number* 50 BD points, then does the horse get to keep those points or does it have to start over with you?
I ask because when I was reading about going affiliated the other day it suggested that you need to affiliate as a pair.
It seems odd to me that you could buy a horse with lots of points and then work it at a high level without having done anything yourself?
Or am I missing something..?
Thanks,
Jo
xxx

[Bay Mare]

(Taken from BD rules 2005)

HORSE GRADING

Points Limit

Prelim: 37 points
Novice: 74 points
Elementary: 149 points
Medium: 249 points
Advanced Medium: 324 points
Advanced: Open to any horse

Horses may compete only at the level that they are graded or higher (unless they have been downgraded).

Grading Points

60 - 61.99%: 1 point
62 - 63.99%: 2 points
64 - 65.99%: 3 points
66 - 67.99%: 4 points
68 - 69.99%: 5 points
70 - 71.99%: 6 points
72% & above: 7 points

RIDER GRADING

Group 1: Riders who have competed CDI or CDIO outside of UK or large tour in a CDIO in the UK
Group 2: Riders who have competed CDI or CDIO in small tour in the UK and/or gained points at Inter I and above in National Classes (Except Group 1)
Group 3: Riders who have won point(s) at Advanced Level and PSG (including FEI Young Rider classes) after 1 April 1994 (Except Groups 1 & 2)
Group 4: Riders who have won point(s) at Advanced Medium Level (including FEI Junior classes) after 1 April 1994 (Except Groups 1-3)
Group 5: Riders who have won point(s) at Medium Level (including FEI Pony classes) after 1 April 1994 (Except Groups 1-4)
Group 6: Riders who have won point(s) at Elementary Level after 1 April 1994 (Except Groups 1-5)
Group 7: Riders who have won point(s) at Novice Level after 1 April 1994 (Except Groups 1-6)
Group 8: All other riders

DOWNGRADING HORSES

Any eligible rider who takes over the permanent ride on a new horse can apply to the British Dressage office, and for a fee of £60, the horse will be regraded for them to ride. This must be done before the horse is competed by the new rider.

Group 7 & 8 rider can downgrade a horse to 60 points
Group 6 rider to 135 points
Group 5 rider to 235 points
Group 4 rider to 310 points

If a rider of a higher grade competes the horse then the points will be upgraded to their peak.

A horse may be downgraded only once in a calendar year.

That's the basis of it but if you want to check out the full rules here's the link:

http://www.britishdressage.org/rules_2005.pdf