Dogs hit maturity around 7 years of age (5 years for larger dogs). It's not uncommon for them to live as long as 15 years. As your pet enters his golden years, his activity level might slow down and common conditions such as arthritis, diabetes, and kidney disease may arise. “It is so more important to monitor the eating habits of older pets,” stresses Tom Carpenter, DVM, president of the American Animal Hospital Association. “Generally, older pets do not need as much protein, sodium, and phosphorus. But your veterinarian needs to address this for your individual pet,” he says, adding that semiannual vet visits are recommended for an older animal.
Some mature dogs are prone to obesity. To test whether your dog is at a healthy weight, move your hands along his sides. If you can feel his ribs (but don't see them), he's doing okay. But if you feel a fat covering, or you visibly notice a rounded abdomen, he might be overweight. Exercise is still important for a senior dog, and if he's gained weight, you want to look for a low-fat weight-control food that contains vitamin-rich fish oils (IAMS™ ProActive Health™ Mature Adult is one good choice).
Other mature pets can become finicky eaters and lose weight as they age. 'Very old pets may actually need a more calorie-dense diet,' Carpenter says. Older dogs can lose their sense of smell and have a harder time chewing their food. To make mature dog food easier to eat, you can top their dry food with room-temperature wet food.
If your dog is gaining or losing a lot of weight, slightly decrease or increase his daily feedings. A sudden change in weight or appetite might be a sign of disease, so you should check with your vet. Water is also essential. 'Older pets are at a higher risk of dehydration,' Carpenter says. Provide a clean bowl with fresh water at all times.

Pregnancy and nursing are not only responsible for many changes in a dog's body, but for changes in her lifestyle as well. If your dog is pregnant or nursing, pay special attention to her changing nutritional needs as she carries, delivers and nurses her puppies.
If you're planning to breed your female dog, it’s important to assess her body condition well in advance of breeding. Because of the physical demands of pregnancy and nursing, a dog with less-than-ideal health can experience problems:
Be sure to feed the proper amounts of a complete and balanced diet. This will support the mother's healthy weight and body condition before breeding and help maintain her health and that of her babies throughout pregnancy and lactation.
The gestation period for dogs is nine weeks. Pregnant dogs gain weight only slightly until about the sixth week, and then gain weight rapidly.
The energy requirements of pregnant dogs are reflected in the pattern of weight gain. Pregnant dogs will need to consume 25% to 50% more than their normal food intake by the end of pregnancy, but energy requirements do not increase until about the sixth week.
The best diet for pregnant and nursing dogs is a high-quality, nutrient-dense pet food formulated for all life stages or for growth. Although puppy diets are generally recommended for pregnant or nursing dogs, large-breed puppy formulas may not be appropriate for this use due to their adjusted energy and mineral content.
Pregnant dogs lose weight after giving birth, but their nutritional needs increase dramatically. Depending on litter size, nursing dogs might need two to three times their normal food requirement to nourish their pups. Be sure your nursing mom has plenty of water so she can generate the milk volume she needs to feed the litter.
To help your nursing dog get enough nutrition, you can try several tactics:

By four to five weeks after birth, most puppies are showing an interest in their mother’s food. Gradually, the puppies will begin eating more solid food and nursing less. At the same time, the nursing mother will usually begin eating less. Most puppies are completely weaned around age 7 to 8 weeks. By this time, the mother's energy requirement is back to normal, and she should be eating her normal pre-pregnancy diet.