Ask. What have you got to lose? In the worst case, you have to continue to use your holidays. But any half-decent company should allow it.
If it's a week or less per year, and you're not asking for the cost of the conference itself, I wouldn't have any issue with it. The improvement in your morale from personal improvement would be enough to justify the time.
If you were asking for the conference then you'd have to tell me what the company gains from it. But it wouldn't be a difficult sell. In all the times I've lobbied for this kind of training for people who work for me, I've never been rejected.