Letters of Recommendation / Evaluation are an important portion of the veterinary school application. You should familiarize yourself with the types of letters of evaluation each vet school requires well before you head into the application cycle.
The Veterinary Medical College Application Service (VMCAS) requires a minimum of three electronic evaluations and allows a maximum of 6 recommendations to be electronically submitted. If there are strong preferences of types of letters, it will be indicated. If the school does not give any guidance about the letters they expect, the “model” typically followed by applicants are one hard science professor, one veterinarian and another “professional” reference. This can come from another veterinarian, a research mentor, volunteer coordinator, employer, etc.