Other than the decision to attend vet school (and what school to attend), the decision whether to seek an internship versus other options (residency/specialization, academia, entry into private practice) is the most important decision you will make in your career. It will define you as an individual who knows what species you most want to work with and will demonstrate to all future employers that you were dedicated to your decision and knew what it would take to become a proficient and respected practitioner.