It is important to remember that, like human medicine, veterinary medicine is an enormous field, and your veterinarian cannot be an expert on everything. Because of this, most veterinarians are very comfortable with your seeking a second medical opinion. In fact, your vet may even recommend this option, especially for a particularly difficult or unusual problem. Your vet may refer you to a local specialist or to a veterinary teaching hospital (if there is one in your area), because these resources offer a great deal of additional expertise in specialized areas (eg, neurology, cardiology, oncology, etc). Such expert consultation may involve significant added cost but is often the most effective way to get to the bottom of an unusual problem and obtain the best treatment.
A couple of notes of caution are warranted about seeking expert advice from books or online resources. Print resources, Web sites, and online pet-friendly forums can often provide you with general background information. However, sometimes the information is inaccurate or by nature incomplete, and these resources should never be considered a substitute for the skills of a qualified veterinary professional. A vet who has taken your pet’s history and performed a physical examination is in the best position to diagnose, recommend additional testing (if necessary), and treat your pet’s problem.
**Adapted from webvet.com