Many pets do well on commercial diets most of their lives. Suburban Animal Clinic recommends Science Diet, Purina One/Purina ProPlan, Iams or Eukanuba pet foods. These are nutritionally balanced and divided into life stages (puppy/kitten, adult, and senior) so each life stage receives the proper nutrition. We won't go into natural or grain free foods-that's a whole other topic.
There may come a time, however, when a pet, for a variety of reasons, may require a specific prescription diet available only through a veterinarian. There are diets for allergies, kidney disease, liver disease, diabetes, arthritis, urinary disease (ie cystitis, urinary stones), gastrointestinal upset/disease, IBD, and even for obesity. Why, there's even a special diet for cats with thyroid disease (not dogs though).
Why would a vet recommend a prescription diet? The answer is because the diet is specially formulated for pets with that specific health problem. Kidney diets have lower protein and sodium to aid in kidney function. Diabetic diets have lower carbohydrates, while obesity diets have fewer calories and higher fiber content to help the pets feel fuller. Urinary diets can aid against the formation of crystals or cystitis in pets who are prone to such. Gastrointestinal diets are bland and easier to digest.
A prescription diet doesn't necessarily mean no other medication is needed. There are cases i which the pet can eventually discontinue other medications. But there are many cases where the prescription diet is meant to supplement the work done by certain medications and other supplements. If the veterinarian recommends a prescription diet, it's because he or she feels it would be more beneficial for your pet instead of continuing with a commercial pet diet.
Some health concerns also benefit from increased water consumption, making the canned version of these diets a good idea. Some canned diets come in patte form (one big chunk you cut up), while others also offer a stew consistency. Many feline diets are beginning to offer a chicken flavor as well as a fish or tuna flavor.
One of the bigger controversies with changing to a prescription diet is for pets with allergies. If a pet is suspected of having a food allergy, it must be put on a food trial for a minimum of 6 weeks with zero outside food or treats. That new food must have a protein and carb source the pet has never been exposed to. Most commercial pet foods contain some form or other of chicken, beef, and for cats, seafood. So prescription allergy diets often come in venison, duck, rabbit (for cats), or even a hydrolyzed protein so the pet is guaranteed never to have been exposed to that protein source before. Ingredient label reading is essential for allergy pets!
Suburban carries several commonly prescribed prescription diets, and can order any Hills or Purina veterinary diet (Royal Canin can be ordered as well). For more information on Precription Diets, visit Purina @ https://www.purina.com/products/purina-pro-plan-veterinary-diets
or
Hills @ http://www.hillsvet.com/en/us/home.