Hiiii tamilarasan!!! The eligibility criteria for admission in veterinary is that you should have a minimum aggregate of 50% is enough to sit in any entrance exam which is held for admission in any veterinary College like AIPVT

Basically 12th board marks has no value.  It is just a milestone to prove that you know something and are eligible to study ahead ( higher order studies I mean)  segregation 75% is done for the same purpose.
You need to give some state level or National level examinations for the better future ahead
Hope this helps
Thanks