These days most commercial food take all this in consideration. Just make sure you choose the right type of food for the right type and age of the dog. But if you would like more information these are the theories it is based on.
Although, in theory, the needs of any individual dog can be estimated by the use of charts and tables, it is equally easy to weigh a dog at intervals. Having ascertained the optimum weight of every dog in the kennel when in fit condition and in perfect health it is as well to record this, and then one may decide whether excess weight demands less food, more exercise, or both, loss of weight indicating a need for extra nourishment. It is soon possible to get to know the sort of food each dog requires and thrives best on.
Increased weight may be due to growth, excessive fatness, muscular development, or even to the over-retention of fluid in the tissues. It may also be associated with pregnancy or with pyometra in the bitch, or in either sex with any dropsical condition. In the two latter, the distension is purely abdominal with increased girth and there may even be loss of flesh in other parts of the body.
It is easier to put on weight than to reduce it. A tendency to obesity appears to be hereditary in some lines, especially among bitches. Excessive fat can be gradually reduced in a healthy subject by increasing the amount of exercise and cutting down on carbohydrates and fats. Lack of body fat may sometimes require a veterinary examination to determine the cause.
In a healthy, worm-free dog, the weight may be increased by extra food containing the essential proteins and carbohydrates and fat, plus the necessary minerals, vitamins, and trace elements in the right proportions.
Exercise needs to be moderated though it must be sufficient to keep the muscles in good trim. Care should be taken to distinguish the abnormally lean dog from one in a state of hard muscular fitness. The lean dog may be very fit and healthy but the over-fat one may be a sick clog in spite of its prosperous appearance.
The energy value of a food is usually expressed in calories; another way of showing how much body heat a particular food is capable of producing. A calorie is the unit of heat that will raise the temperature of one cubic centimetre of water one degree Centigrade.
The heat output of the animal at rest, expressed in calories, is known as the basic metabolic rate. As a result of numerous experiments carried out by many investigators it is now accepted that the requirement of a dog weighing 13.5 kilograms (about 26 lb) is 24 calories for each pound body weight per day. A clog of Cocker size, say 25 lb, would therefore (in theory) require 600 calories daily in terms of food.
This figure, however, was worked out using experimental dogs at rest, and allowance must therefore be made in every case with due regard to the amount of exercise or work, and an appropriate number of calories added to the amount. This is where theory and practice are apt to get a little tangled. A sheepdog on the hills may easily travel 20 to 25 miles in a day, but a Pekingese or a Chihuahua might not do a great deal more than that in yards.
Extensive experiments have shown that the requirements of the normal housedog may average 4.0 calories for every pound of body weight. On 50 calories per lb (100 calories per kg) most of the experimental dogs put on overweight.
What applies to pets and housedogs in general, does not apply to hounds and working dogs, which could consume more than 5o calories per lb bodyweight and still remain lean and fit (provided they were working).
The number of calories considered requisite to retain condition in the housedog needs to be increased in growing dogs, also during cold weather, and in pregnancy, and in lactating bitches.
In estimating the number of calories required, body surface is actually more important than weight.
In a small breed, such as a Chihuahua or Yorkshire Terrier, the basic metabolic rate is inversely proportional to that of a large dog such as a Great Dane or Pyrenean, since in dogs with a large body surface there is far greater loss of body heat.
Growing puppies require twice as many calories for each pound of their weight as adult clogs would need. Arnold and Elvelyem determined that a puppy weighing 21 oz required 282 calories, but as soon as it attained the weight of 10 lb it would require only 900 calories through an entire day.
Allowing 40 calories for each pound body weight, this would feed a 30 lb house- dog for a day and permit it to take normal exercise.
Alternatively, a diet containing an almost equal number of calories could be provided by 4 oz of tinned dog food (200 calories), 4 oz biscuit (400 calories), and to oz of milk (zoo calories) with 4. oz wholemeal bread (28o calories.)
The above examples show how, with a knowledge of food values, the changes may be rung to provide a varied diet and, on occasion, practice economy. Due account will have to be paid to (a) palatability, (b) digestibility and (c) bulk.