How do dogs' nutritional needs change as they age?

A mother's milk provides all a puppy needs up to about four weeks old. It's around this time that puppies can begin to be weaned for a period of one or two weeks. You may be surprised at the amount of food a little puppy needs to maintain its rapidly growing body. Per pound of body weight, puppies need to eat about twice as many calories as normal adult dogs [source: National Academies]. They also need more proteins and fats than adult dogs. Especially for bigger dog breeds, you must be careful that the puppy isn't growing too quickly, because of the stress this can put on bones, joints and organs [source: Becker].

So, what does this boil down to when you're faced with the different varieties of puppy food in the pet store? Experts lend some suggestions to help you decipher what some of the labels mean on these foods. Some puppy food, for instance, isn't specifically formulated for a puppy's diet, but happens to meet the minimum nutritional needs of a puppy as determined by the American Association of Feed Control Officials (AAFCO). At the very least, the food you choose should say on its label that it meets these. But foods that merely say they "meet" these requirements are not as preferable as those that boast balanced nutrition "based on AAFCO feeding trials," or something similar [source: VMRCVM].

Although puppies need a lot of food, you should avoid having food out for them all day so that stay at a healthy weight. You can do this by measuring the food you give them (based on the food label or a vet's advice) and feeding them two to four times a day at regular, consistent feeding times. By the time they're about six months old, you can reduce the frequency to two meals per day.

The puppy stage passes all too quickly. After about a year (depending on the breed), your dog can completely switch to an adult diet. However, you should avoid upsetting a dog's digestive system by performing this change gradually. Start by mixing in just a little adult dog food into the puppy food, and increase the proportion of adult food a bit more every day.

In addition to size and breed, a lot of a dog's nutritional needs will depend on its activity level. Because of their increased energy needs, active dogs need to eat more calories. But it's not simply a matter of feeding them more of the same food. That's because active dogs also need a higher percentage of protein and fat from those calories. Compared to sedentary dogs, very active and performance dogs may need about twice the percentage of calories from fat [source: Becker].

A good way to determine if your dog is eating a healthy amount is to keep an eye out for signs that the dog is underweight or overweight. Underweight dogs look emaciated, with very visible ribs, vertebrae and pelvic bones. It's healthy to feel at least a layer of fat under its ribs. If you can't feel the ribs at all, or only through a very thick layer of fat, this is a sign that the dog is overweight -- a more common problem for dogs with plenty of access to food. An overweight dog might need to be put on a low-calorie, low-fat and low-protein diet. Because of a dog's tendency to overeat, as well as the need for a nutritionally balanced diet, limit treats and table scraps to no more than 10 percent of a dog's daily intake of food [source: VMRCVM].

Some dog owners assume that because vitamins and minerals are so essential, there's no harm in adding supplements to a dog's diet. But this isn't the case. Unless a veterinarian recommends specific supplements, there's no need to add them to a dog's diet. It might actually cause harm, such as upsetting the dog's delicate balance of calcium and phosphorous. In addition, some potential toxins to avoid are onions and garlic, as well as grapes and raisins. Chocolate is notoriously toxic to dogs as well.

When it comes to the changes in diet at different life stages, we can't overlook the importance of pregnancy. In order to keep the expecting mother and her puppies healthy, you'll need to provide her with a special diet. Pregnant dogs gain about 20 to 50 percent of their normal weight during pregnancy, but this weight gain usually doesn't begin until the fourth week. So, that's around the time you should start feeding her more food than usual. Keep in mind that if she's carrying a big litter, there'll be less room for food, so this will require more frequent, smaller meals to keep up with her needs. Specifically, she'll need about a third more food than usual at the fourth week [source: Olson]. Meanwhile, as the pregnancy progresses, the amount of food she needs will only increase.

One of the most important elements of the dog's pregnancy diet is high-quality protein -- that is, protein that is easily digestible and provides the right amounts of all the essential amino acids. If you use dry dog food, it should contain around 27 percent protein (because it has water, the equivalent for canned is only 8 percent) [source: Rice]. This protein will work toward forming healthy, strong tissue in the developing puppies while in utero. Some experts recommend vitamin and mineral supplements during pregnancy, but you should talk to your vet before starting these.

The special dietary needs don't end with birth. Remember that a lactating dog still has to provide all the nutrients to her young puppies outside of the womb for about four to six weeks. In fact, she may need even more food than when she was pregnant. The best diet is one rich in animal protein and fat. These will help her with milk production.

You may not be able to teach an old dog new tricks, but you'll have to get it used to a new diet. Older dogs tend to become overweight. This is a natural result of a slowed metabolism that comes with age. It only contributes to the problem when pet owners fail to take account for this and don't adjust their dog's diet accordingly. It's understandable that some owners hate to think about the fact that their dog is getting on in years, but it's best for the animal to adjust its dietary needs.

Because of this slowed metabolism and reduced activity and exercise, older dogs require fewer calories. Specifically, they need about 20 percent fewer calories than the average adult dog [source: National Academies]. And, to aid their digestive system, they benefit from a diet with additional fiber. You may notice several senior dog foods that boast low amounts of protein. However, unless your vet recommends a low-protein diet for a condition like liver or kidney failure, don't assume that your dog will benefit from it. In fact, many experts say older dogs need even more protein than younger adult dogs to keep up their protein reserves. The need for high-quality protein is probably even more important at this stage of life, since it's more easily digestible.

Due to sensory loss that comes with old age, senior dogs may not have as big of an appetite as they used to. If this gets so bad that they're no longer maintaining a balanced diet, you can try tempting them with different foods or heating up their meals [source: Becker]. And because maintaining water balance gets more difficult for their aging bodies, always have water available to them [source: Kam].