What is a horse carrot? Or do you mean large carrots?
Yes 1 to2"
Same way you grow regular carrots. If you have horses, I would space out my crops at 2 week intervals so you have production all season long. And hopefully a decent root cellar for storage.
Here's a post that might help you - https://www.horseandhound.co.uk/features/grow-horse-treats-guide-green-fingered-688829
Here's a link on growing carrots, it applies to any kind of carrot: