Is your son undecided about whether to go for a DVM or to go into marine biology? I would think that the requirements would overlap enough that this would most likely be a decision that could be postponed until he has a chance to get more experience with both.
We have a daughter who is currently enrolled in a DVM program, so I can certainly comment on aspects related to veterinary programs (including getting into them). She did her undergrad at UVM with a dual major, including animal science as one of the majors. There are also a few other parents on this web site who have kids in DVM programs.
The CREAM program at UVM is very good. I expect that UNH is similar. You do need to get accepted into it. However, if a student’s grades and relevant experience are sufficient to have a reasonable shot at DVM programs, then I expect that they would likely get in. The farm is not all that far from the campus which is handy.
We visited all of UNH, U.Mass, and UVM multiple times. They are all very attractive campuses. I think that any of them would be very good for a pre-veterinary student.
When our daughter started in her DVM program, there was an opening ceremony that we got to listen to. They said where each student had graduated from. The students in at least one (top 5) DVM program come from a very, very wide range of undergraduate universities. Out of well over 100 students, I did recall hearing a couple of schools mentioned twice, but I do not recall hearing any school mentioned more than that other than the DVM school itself (and even it was where only a handful of students got their bachelor’s).
DVM programs are expensive. My daughter has mentioned a few times that most of the students in her program are taking on too much debt to get their DVM. If your son wants to seriously keep open the option of getting a DVM, he should at least avoid debt for his bachelor’s degree. Having some $$ left in the college fund for the DVM program would also be a good idea. My understanding is that for someone interested in marine biology a master’s degree is a good idea, and again it is a good idea if reasonably possible to leave some $$ in a college fund for this also. If staying in-state saves money, it could help a lot when it comes time to get either a DVM or a master’s degree.
And yes, pre-vet is an intention, not a major. If you want to get in a DVM program, then you need to complete the pre-vet requirements while maintaining a good GPA and getting a bachelor’s degree in something. I would expect that marine biology requirements and pre-vet requirements probably overlap enough to make marine biology a reasonable major for a prevet student.
Pre-vet classes and premed classes overlap a lot. Many of my daughters friends, that she met in undergraduate pre-vet classes, were premed students (one got her MD this past May). Premed / pre-vet classes are in some cases very academically demanding. There will be a lot of very strong students in these classes at any of the schools that you mentioned (including U.Maine and UNH). There will be tough exams at any of these schools.
Experience in a veterinary environment is very important to get accepted to DVM programs. Students can get this either while an undergraduate student, or after getting their bachelor’s degree before applying to DVM programs, or both (my daughter went with “both”). My daughter and I both think that her experience and the resulting references were the most important thing in her getting multiple acceptances to DVM programs.
I agree with @Pathnottaken about attending an admitted student’s day at UNH. It is an attractive school in an attractive location. It has both the CREAM program and marine biology as options. Saving money for graduate school of one type or another is important. Pre-vet classes there will be academically demanding and will have strong students. I also agree that if a student is living on campus, it is an entirely different world compared to living at home. This is true even if the campus is only one or two miles from home. Then if something goes wrong, help can be nearby. Bad breakups and/or flu can happen even to a university student.