Basics of Nutrition: Nutritional Protein Guide for Dog and Cat Owners.

Proteins are complex molecules, and they are building blocks of animal tissue. They are made of carbon, hydrogen, oxygen, and sulfur. Proteins are rich in nitrogen and sulfur. 

The nitrogen balance test is used to estimate the net loss or gain of body protein reserves. In this test, the amount of nitrogen is measured in both food intake and excretion. The difference indicates a net loss or gain of protein reserve in the body. 

Amino acids are the building blocks of proteins. The amino acids are linked with peptide bonds. The sequence of amino acids impacts their functionality. For example, the amino acid sequence dictates protein folding and its functionality. 

Albumin in blood plasma, lactalbumin in milk, zein in corn, and structural keratin, collagen, and elastin are examples of proteins. 

Nucleoproteins, glycoproteins, and phosphoproteins are complex forms of proteins, and they are attached to non-protein molecules. 

Proteins have various functions. They form hairs, nails, muscles, blood, and much more. 

Enzymes are also made of amino acids, and they are proteins. They serve specific functions in the body. Many hormones are proteins, such as insulin and glucagon, both of which regulate glucose levels in the blood. 

Proteins can be degraded and resynthesized in the body with essential and nonessential amino acids. 

Essential amino acids have to be acquired in the diet. 

Nonessential amino acids can be produced in the body if adequate nitrogen is received from the diet. 

 

Proteins are also a good source of energy in the body. It is 3.5 kcal/gram. The excess protein in the body can be stored as either glycogen or fat in the adipose tissue. In the diet, proteins and amino acids also provide palatability in the food. They can also react with food compounds like fat and carbs to create new flavors. 

However, not all proteins are equal. Some are more digestible. Hydrolyzed proteins can have higher bioavailability. Dogs and cats can also develop allergies to certain proteins. Therapeutic diets may include expensive protein sources such as hydrolyzed yeast. 

Here is some formula to determine protein quality in diet: 

Chemical Score: 

Egg protein is often used as a reference for protein digestibility. It has the highest score of 100, and its amino acid sequence is utilized to indicate its chemical score.  If certain essential amino acids are missing in a diet or in a protein, it is a limiting factor for protein deficiency. It is also called a limiting amino acid. 

Methionine, tryptophan, and lysine are three amino acids that are usually limiting amino acids. Therefore, pet nutritionists may want to add these amino acids into diets as free amino acids in the form of salts. For example, the poultry industry heavily relies on these amino acid salts to support the growth of young birds. 

Essential Amino Acid Index: 

This method focuses on the total amount of essential amino acids rather than limiting the one in greatest deficit as in the chemical score. It is also an indicator for total essential amino acids. It is a geometric mean calculation. 

Total Essential Amino Acid Content: 

The method is focused on the total essential amino acid content to total nitrogen in certain food. The method emphasizes the total essential amino acid content. This measure is different from the chemical score and the essential amino acid index. 

Important note: focusing on the amino acid composition can be misleading because processing conditions may impact the bioavailability of amino acids in food. For example, heat can impact bioavailability. 

Therefore, a nutritionist needs to perform feeding trials. 

Protein Efficiency Ratio: 

It is the most commonly used and simplest feeding trial test. The animals are fed with a certain amount of test protein for up to 28 days, and the grams of weight gained by total grams of protein consumed is calculated. PER value indicates the ability of a protein source to be converted into tissue in a growing animal. 

This method is very consistent with rats, but it may not be consistent with dogs and cats. To improve this test, nutritionists can include positive and negative control. Positive control is a diet fed with reference protein (egg). The negative control diet is the protein-free diet. 

Biological Value: 

This method provides more accurate value than protein efficiency ratio, but it is more labor intensive. It is the measurement of how much amino nitrogen is turned into tissue in the body. To find out how much nitrogen is in the body, total nitrogen in diet and excreta must be measured. All pets must be at the same physiological maintenance, and the diet must have enough carbs and fats. However, this method does not account for protein digestibility. As long as protein is absorbed into the body, the BV value will be high. 

Net Protein Utilization: 

This method addresses the limitation of BV calculation. NPU is calculated as the product of a protein's BV and its digestibility. If a food is 100% digestible, it has the same BV and NPU value. If protein has low digestibility, it has lower NPU than BV. 

 

Final Thoughts

Proteins are not just nutrients; they are building blocks of the body and serve physical and chemical functions in the body. They are degraded and manufactured again and again in the body to keep the body running smoothly. There are methods to determine how much proteins provide benefit to the body, but in vitro trials provide the best results.