The risk with this as a long-term diet is the dog may become deficient in certain vitamins and minerals. Dietary deficiencies may not become obvious for months or even years, so there will be a delay before any problems start to occur. With this in mind, if chicken and rice is your choice for a long-term diet, speak to a qualified veterinary nutritionist about a recipe or supplements that are appropriate for your dog's age, size, and health issues.