I think you get 8k exp per 1 zeal, I'm not 100% sure. Let me go check now!
EDIT: Sorry, I was mistaken. At level 1, you only get 7 exp per zeal in slayer, but in prayer you get 15 at level 1, and 29 xp at level 1 in defence.
I have 0xp in all three of those skills too.