Hi Cameron,
A wee bit of googling should sort you out, but
this is a good place to start.
"SQA Highers and Advanced Highers
Candidates are required to take a sixth year and undertake Advanced Highers.
* AAABB at Higher to include Chemistry and two of Biology, Maths, Physics - including AA in Chemistry and one other science subject.
* BB at Advanced Higher in Chemistry and another science subject.
* If possible Advanced Higher Biology, as this will be beneficial for the first year of the course.
* If Biology has not been studied in fifth year, it should be taken in sixth year to Higher level.
* If Physics has not previously been studied to Standard Grade or Higher level, it should be studied in sixth year to either Standard Grade, Intermediate 2 or Higher level.
All grades must normally be obtained in one sitting and at the first attempt.
But, I'm only posting the above, so you don't think the next bit is too patronising (I hope!!). Yes, you need the grades, otherwise you won't get in - simple! However, for a course as over-subscribed as vetting, you need something else as well - a spark about you that the admissions people can see, and that sets you apart from the rest of the crowd.
My Sister is a vet, and what she did to get in was to spend her weekends and holidays in the years between standard grade and SYS getting as much experience as she could in all sorts of vetty things. For example, she managed to get work experience with the local vet, and abbatoir (yuk!, but it teaches you a bit about anatomy, and it did impress the admissions folks). She also worked weekends at a local farm and cattery, volunteered at the local RSPCA centre, and generally got as much experience as she possibly could.
Basically this approach worked. By the time she went for interviews at Universities, she could show that vetting was something she'd considered carefully, found out a lot about, and was still dead keen on (there's nothing worse than getting half way through a uni degree and finding out you've picked the wrong thing, so doing some homework to make absolutely sure beforehand is a great idea). This put her a long way ahead of the folks who'd just held vetting as a vague notion up until the point they filled in their UCAS forms.
Hope that helps, and good luck!!