It's necessary.
Anything with protein (meat), Fish and chicken
Protein is used by the body to build muscles, but is also a food supply for cells. Animals obtain most of their protein by feeding on other animals and plants.
animals all animals (meats) have protein, some plants have protein too, like peanuts.
Animals obtain their energy and carbon from the food they ingest. Carbohydrates and protein are a good source of carbon and energy.
The common protein found in all animals is collagen.
Meat and milk and protein
comparing the weight gained in lab animals consuming a test protein with the weight in lab animals consuming a standardized (reference) protein
Animals source their protein from various sources in their diets, including plants, other animals, and sometimes from insects or microorganisms.
Foods rich in high protein are a good match for you. Deep ocean fish and vegetables have high protein. Dairy is another good choice, as long as it is from organically grown animals.
No
Except for the protein that is used by the animal, protein can be lost in several ways. For example, if the animal has a problem with digestion or absorption, protein can be lost via the faeces. Protein can also be lost into the abdomen, and animals with kidney malfunction can lose protein via urine (eg. a protein losing nephropathy).
Collagen