For years, veterinary medicine has been a field with a limited number of slots for students and, theoretically, good career prospects. But after years in which enrollments have grown and the numbers of pets and veterinary visits in the United States have declined, new veterinarians are facing a debt crunch, The New York Times reported. Salaries have fallen, and the average debt to income ratio for new D.V.M.s is now twice that of M.D.s.