Dogs and cats are members of Carnivore order, but the dog is described as an omnivore, while a cat is a true carnivore. Cats can not produce nutrients such as (Vitamin A, arachidonic acid, and taurine, etc) from plants. They exclusively depend on eating meat to get its nutrient. Feeding is one of the most important management practices of the pet owner. In addition, nutritional management is increasingly recognized as an integral part of both preventive health care and treatment protocols for medical and surgical patients. The simplest method of meeting and nutritional requirements of dogs or cats is to feed a fixed formula, complete and balanced commercial diet designed and appropriately tested for dogs and cats. However, dogs and cats can thrive well eating a variety of commercial or homemade foods, which may include vegetables and synthetic supplements.

Dogs are a biologically diverse species, ranging from 4 to 80 kg (2 to 175lb) in body wt. normal birth weight of pups depends on breed and ranges from 120 to 550 g. The growth rate is rapid for the first 5 mo, and pups gain on average 2-4 g/day/kg of their anticipated adult weight. The growth rate begins on plateau after 6 mo, and growth may be completed by 9-12 mo of age in small breeds and by 12-18 mo of age in large breeds. The average mature body weight of domestic cats is 3.2+/-0.9 kg (7+/- lb) for toms, and rate is exceptionally rapid for the first 3-4 mo, and kittens gain 50-100 g/wk. The growth rate begins to plateau at 15-160 days of age, and growth is completed within 200-220 days.

Body condition scoring is used in many species to provide a rough guide of the nutritional adequacy of the diet and the level of food intake of an animal. Dogs and cats should be weighed and a body condition score of 1-5 assigned as follows: 1) Emaciated: Ribs, lumbar vertebrae, pelvic bones, and all body prominence evident from a distance. No discernible body fat. Obvious absence of muscle mass. 2) Thin: Ribs easily palpated and may be visible with no palpable fat. Tops of lumbar vertebrate visible. Pelvic bones less prominent. Obvious waist and abdominal tuck. 3) Moderate: Ribs palpable without excess fat covering. Abdomen tucked up when viewed from side. 4) Stout: General fleshy appearance. Ribs palpable with difficulty. Noticeable fat deposits over lumbar spine and tail base. Abdominal tuck may be absent. 5) Obese: Large fat deposits over chest, spine, and tail base. Waist and abdominal tuck absent. Fat deposits on neck and limbs. Abdomen distended.