taking earned leave for visiting abroad mandatory or casual leave is enough?

For visiting abroad for a period of 5 days, taking earned leave is mandatory or casual leave is enough?

Hi,
In general the commonly followed practice among companies is that casual leaves are restricted to 2-3 at a stretch. So Earned leave will be ideal.
Additional information is when an employee leave out of country he should intimate his employer officially before his travel period.

casual leave for the reason of casual in nature which may be of one or two days.

It is not clear whether you are in private or public employee. In public service CL is considered to be duty period, not period spent on leave. As such, if a Government employee, it is advisable to avail EL.