Probably a roughly equal amount relative to the percentage that apply to the specialty. I.e., if 20% of the applicant pool is DO to a certain field and the program takes 10 residents, about 2 per year on average makes sense, right? But if it’s 7 DOs and 3 IMGs and they’ve only had 1 USMD in the past 5 years, that means there’s something about the program that makes people not want to go there.
While people like to act that it’s a reflection on the training offered, it could easily be something like location. For instance, Case Western and CCF have DOs all through their programs. It’s not because the trainings bad. It’s because it’s location makes it less competitive. So you have to think about it. I matched into a good program. But likely only because the location isn’t very desirable.
Nevertheless, the thoughts about not mingling with peasant DOs is pervasive. I’ve heard of MD students being mocked by their peers for matching a competitive surgical subspecialty because there’s DOs in their class/program.