Protein is best known for supplying amino acids to build hair, skin, nails, muscles, tendons, ligaments, and cartilage. It also plays a main role in hormone production.
The protein in dog foods can be supplied by animal sources, plant sources or a combination of the two. High-quality animal-source proteins contain all of the essential amino acids dogs need, while a single plant-based protein might not contain adequate amounts of some essential amino acids.
Common animal-based protein sources used in pet food include chicken, lamb, fish, and beef.
Even though they are often fed plant-based diets, dogs are not herbivores. While dogs are technically considered to be omnivores—animals that eat both animal- and plant-based foods—they should be treated primarily as carnivores to better fulfill their specific nutritional requirements.
Dogs are members of the Canidae family. This family also includes the wolf, coyote, fox, and jackal. The ancestors and relatives of today's common dog hunted animals and ate them as a means of survival.
The body structure of domestic dogs is similar to that of their ancestors and relatives and is ideal for eating prey. Dogs have the enlarged carnassial teeth after which carnivores are named. Their gastrointestinal tract is simple and does not have the capacity to digest large amounts of plant products.
Animal-based proteins help dogs achieve optimal health.
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.