that seems like such a funny question to me - there are horse farms and breeders all over the state - the show circuit is here also
New Hampshire - Horse Boarding Stables indexed by City + County - A to G
I would check with realtors in that area for horse farm info as it comes around - they are out there.
There's the Valerie Engler farm in Campton and Dartmouth has an equestrian program at the Morton Farm in Etna.
Dartmouth Riding Center Home Page - Show Schedule (broken link)