Keratex is very good for helping protect hooves from chipping or splitting

I use it on my mare and it works a treat

Always farriers formula is very good in the horse's feed!

Hoof oil may work but you can buy specific hoof moisturisers which do the job better. Something like....

http://www.stablemateuk.co.uk/buy-on-line/hoof-moisturiser-300gm/prod_11.html

I haven't ever had to use hoof moisturiser so i don't know the best products to use but a little bit of research and you should find an effective product for your pony :)