I am assuming that you are currently a high school student. Let us know if this is not correct.
To become a wildlife veterinarian, you first need to become a veterinarian. One daughter starts vet school in September, so we have some experience with this.
I am not convinced that there is much to gain from attending a “top 20” university for undergrad if you want to become a veterinarian.
One issue is that the top universities for animal science and DVM programs are usually not the top universities overall. For example UC Davis has the #1 ranked DVM program in the world. It’s overall ranking according to US News and WR is #39. Colorado State University is #3 in the US for DVM programs and #4 worldwide. It has a superb DVM program. USNWR has it ranked #153 overall in the US. Top ranked universities are often in cities (Harvard and MIT being examples of this). Top ranked animal science programs and top ranked DVM programs usually have farms, which are often not in cities.
When our daughter was applying to DVM programs, I looked at where accepted students at a few top programs had done their bachelor’s degree. Generally the accepted DVM students had come from all over the place. You can attend any one of a very wide range of universities for your bachelor’s degree and still get accepted to a top DVM program.
Of course this is largely good news. It suggests that getting accepted as an undergraduate student to universities that have very good animal science programs is not necessarily as insanely competitive as getting into a “top 20” university in the US.
Another issue is cost. If you want to keep open the option of becoming a veterinarian, then you need to budget for a full 8 years of university. The last 4 years are going to be expensive. For example, the in-state cost at CSU for their DVM program show a total cost of attendance a bit over $60,000 per year, and this is IN-STATE. It is over $80,000 per year if your are out of state. Prices usually go up from year to year. One big implication of this is that you want to completely avoid debt for your bachelor’s degree if you want to keep open the option of becoming a veterinarian. This is very likely to point you to in-state public universities. There are a lot of cases where in-state public universities have very good animal science programs.
Our daughter did very well in her various applications for DVM programs, with multiple acceptances and only one rejection. I think that a very large part of this success did come from her experience working in a variety of veterinary situations. This includes working in veterinary offices, working on farms, working with people, and doing some animal research (no animals were harmed in the research that she did).
I agree with @aunt_bea that you should be looking for opportunities to volunteer with a local vet. Our daughter did however also do some work while she was in high school on a farm not all that far from where we live. Volunteering (or getting a job) on a farm is a useful thing to do.
If you want to be a veterinarian, things like reaching inside a cow and cleaning up animal waste become “impressive” extracurricular activities!