The UAI for vet science depends on the university. Sydney is 98.5+, University of QLD I believe is around the same, and murdoch (Perth) , melbourne and adelaide all now require high UAI scores as well as the completion of a pre-vet year (normally 1st yr bachelor of science) at which point they then select students to go onto vet (so not everyone that completes the year will go through), and adelaide has a pre-vet stream of the animal science degree, which upon completion allows you to follow on with their vet science course.
The two different university's are Charles Sturt (Bathurst, NSW) and James Cook (Townsville, QLD) which require a high UAI 90+ but also require you to fill out an application form and answer questions, which is another very important part of the application process. In addition Charles Sturt also holds interviews.
Basically, you need a high UAI to be eligible. It is true that you can do a bachelor of science and transfer HOWEVER in no way would I say that it is easy! If you are unable to gain the UAI needed to get into the degree you seriously need to assess wether you could realistically obtain a distinction average in the 1st year of your science degree in order to transfer. Some students can do this, but on the other hand I know a fair few people who haven't been successful in transferring and were then stuck in a degree they didn't really want to be in. In addition to this many universities will require you to do other things to transfer, such as sit another exam for Sydney and show how dedicated you are to vet by previous and current work experience etc.
Traditionally the larger and older university's have been considered the "best" for veterinary science - Sydney, Melbourne, Queensland, Murdoch. However the newer schools, Charles Sturt, James Cook and Adelaide in my opinion are just as good. I am a bit biased as I'm in my 3rd year of vet at James Cook, but each university has its different pros and cons. The older universities have large established networks and facilities, which are always a bonus, but the newer uni's have brand new facilities and have equally talented teachers and lecturers. The biggest difference I see is that essentially the university's in the city have limited access to larger animals (you can't exactly have a whole lot of cattle in the middle of sydney!) but Charles Sturt and James Cook are able to have stockyards and a farm on the campus making a wider array of animals available for teaching purposes all the time. Hence it seems that compared to my friends at Sydney I have done more cattle/sheep work than they have and they have done more cat/dog work than I have, simply because of what's accessible at the time. HOWEVER each degree has to be accredited by the veterinary accreditation board, who ensure that the curriculums of the universities are equal - hence by the end of our degrees, regardless of what uni you go to, we all have to know the same stuff about the same animals.
Vet is an awesome thing to study at uni and its a fabulous degree, so if you are interested i'd really encourage you to study very very hard and have a look around at all the universities! Its a very tough and demanding degree, but it is really rewarding!
Hope that all helps, if you have anymore questions, feel free to ask!