Life stage feeding is a term used when describing the changing nutritional needs of your dog with age. It is a relatively new term reflecting the increased knowledge obtained regarding our pets physiology.
The puppy phase describes the first 6-12 months and is the major growth phase for the dog. The larger the breed the longer this phase lasts. Puppy food is high in calcium and phosphorus to promote bone health. It is high in calories to provide the energy required for growing tissue. It is really important to feed a balanced diet during this stage to avoid nutritional deficiencies leading to stunted or altered growth.
The juvenile phase follows and lasts 6-24 months of age. Giant breeds are not fully mature until 2 years of age whereas smaller breeds will only be in this growth phase until a year old. In the juvenile phase growth slows down (but doesn't stop) so food doesn't need to contain the high levels of fat and protein needed to assist the rapid growth seen in the puppy phase.
Adult food is aimed at dogs 12-24 months of age (depending on breed size) onwards. It is a well balanced diet with fewer calories than puppy or juvenile food and is aimed at maintaining a healthy weight. Neutered dogs have a slower metabolism and therefore lower energy requirement than entire adult dogs so it is worth investing in a low calorie adult food if weight gain is an issue.
The senior phase starts from 8 years in giant breeds to 12 years in small dogs. This reflects the variation in life expectancy. Senior food is lower in calories to take into consideration the reduced activity in older dogs. It also contains a blend of vitamins, minerals and supplements to support the immune system of older dogs. For example glucosamine is often added to support the joint cartilage. Senior food contains less protein as dogs are not in a growth phase.
Finally the pregnant and nursing stage is from the last trimester of pregnancy throughout the lactation period. There is a huge demand for calories during this time so a suitable food is needed to prevent excessive weight loss and enable the production of plentiful high quality milk. From the 7th week of the gestation period onwards a bitches intake should increase by 25% each week. She should also be fed smaller meals more frequently due to pressure on the stomach from growing puppies. Most lactating bitches can be fed ad-lib, especially if they have a large litter.
Any advice on life stage feeding can be obtained from your vet.