I use Paw Card (it allows me to input for all my animals, not just the horses). And Sionna, download JotNot Pro- it essentially turns your iPhone into a scanner and saves anything you "scan" as a PDF file you can email. All you need is the document to be scanned, a flat surface and reasonable lighting. It's the best!
Paw Card doesn't look like it is available anymore. I just got an iphone and was so excited to have apps to track my animals. I downloaded Horse Keeper that seemed to have better reviews than pocket stable.
Oh bummer! I got it almost a year ago I think. I just looked at Rendaivu and really like the look of it, seems more detailed than Paw Card for the horses. I'll probably keep my small animals on it and switch to Rendaivu for the ponies.