All breeds have specific diets - and these diets are usually dictated by evolution and geographical origins. A Rat Terrier is a hunting dog from the US. Its gene pool is wide and varied. It is definitely a red meat eating breed that can also thrive on fresh fruits. It does not fare well on a diet exclusively made of grains and wheat.
Ideally, all dogs should have freshly made food everyday. A Rat Terrier should not be an exception. However, many Rat Terrier owners find it easier to buy a bag of commercial dog food instead. This typical move for convenience contributes to many of the health problems that the average modern Rat Terrier suffers from.
One of the primary concerns with constant commercial dog feeding is overfeeding. The Rat Terrier is tiny in stature. Obesity in the animal is not at all an endearing trait - it is a life-threatening condition that can literally crush your pet's internal organs in the long run.
Commercial dog food has so many preservatives and salt that nutrition is at its minimum. The fact that you don't really know what goes into making these commercial dog foods should be a huge factor in deciding to discontinue using commercial dog food feeding. For example, if the ingredients list beef or pork, would you know whether the beef and pork were quality parts or scraps and gristle?
Obesity also hampers the dog's movement, making it less active and more prone to sickness and degeneration of the joints. A Rat Terrier is a roving dynamo on four legs. Its health will only deteriorate from lack of exercise and mental stimulation. A bored Rat Terrier is a destructive creature, so try to at least keep the pounds off your pet so that the domino effects of obesity do not get triggered.
Ask your vet how often and how much you should feed your pet Rat Terrier. Ask him what foods are allowed into its diet and which are not. Depending upon your dog's health requirements, some vets recommend feeding twice a day, two small portions of a meal. Some vets recommend a healthy platter once a day. The size of an eating platter or serving portion actually depends on the size of your dog. Also, some working dogs or the very active ones consume more calories a day and will therefore need more food.
And please, whatever "junk food" you are eating, try not to share them with your pet Rat Terrier. Some of them contain high levels of salt, sugar, and preservatives. If they don't lead to obesity, your dog may suffer from dental problems or medical problems like diabetes.
Meat is an essential element to your Rat Terrier's diet: chicken (or any fowl meat), pork, beef, and venison are all acceptable sources of meat protein. Fruits and vegetables are also great sources of additional nutrition for the Rat Terrier.
Lastly, try to give your dog lots of drinking water. Do not limit your pet Rat Terrier's water intake to just a cup or two a day. Active dogs need water to cool down on a hot or humid day because they have no sweat glands to help them release body heat.