Years ago when I was a child we were told not to feed the pony apples because she had had laminitis, and the vet said fresh grass and apples encourages laminitis. This is a horrible illness and very painful for the pony and in very bad cases it can cause death. You might be better just to phone your vet and check. Hope all goes well.
Just to follow up, chipchopper, here is a link. It doesn't actually mention apples in this article, just grass, but I don't think I would want to take any chances. http://www.animedvets.co.uk/laminitis.htm