Amino Acids and Proteins

pages 293,297, 298

any additional pages sourced will be noted.

Amino Acids and Proteins• Amino acids are defined as any organic

compound containing both an amino and a carboxyl group.

Amino acids occur naturally in plant and animal tissue and are the chief constituents of protein. Amino acids are broken down into two groups, Essential Amino acids and Nonessential amino acids.

*

Page 297

Proteins• Amino acids are called the building blocks of

protein.• Proteins are essential to all living cells.• Protein functions include:

– Regulation of metabolism– Cell membrane construction– Muscle fiber formation, contraction regulation– Tissue growth and repair

• Proteins also serve as enzymes, hormones, and antibodies.

Proteins are sometimes bound to other substances to form even more complex molecules. For example:

Proteins conjugated with carbohydrates are called glycoproteinsProteins conjugated with fats are called lipoproteins

Species and Growth Stage

Recommended Protein %

Recommended Fat %

Puppy 28% 17%

Adult Dog 18% 9-15%

Performance Dog 25% 20%

Racing Sled Dog 35% 50%

Lactating Dog 28% 17%

There is also a table on page 298 that shows protein values only.

• There are several tests that predict the quality of protein.

• * This information can be found in table 9 – 6 on page 299

• Net protein utilization (NPU): This compares the amino acids composition to a source known to be of a very high quality. Egg protein is typically used as the reference protein as it has been given a chemical score of 100.

• Amino acid score (AAS): This test measures the contribution a protein makes to all of the essential amino acids. This test is a modification of the chemical score test

• Protein efficiency ratio (PER): This is the simplest and most commonly used test. Weanling male rats or growing chicks are fed an adequate diet containing the test protein for 28 days and changes in weight are measured. PER is calculated by the amount of weight gained divided by the total grams of protein consumed.

• Biological Value: This is the percentage of absorbed protein retained in the body. It is a measure of the ability of the body to convert absorbed amino acids into body tissue. Nitrogen in the food is measured against the nitrogen in the feces and urine.

Protein Values

• High quality protein is especially needed during:– Periods of growth– Physical exertion– Pregnancy– Lactation– Repair of damaged tissues

Amino Acids

• They are not stored in the body like fat and carbs. If not consumed in required levels, breakdown of protein in the viscera and skeletal muscle will occur. This breakdown in protein provides amino acids for energy. The breakdown of circulating and structural protein into glucose is call gluconeogenesis.

Signs of Protein Deficiency

• Decrease of muscle mass• Weight loss• Dull hair coat• Anorexia• Immunodeficiency• Poor mentation• Generalized edema• Death

Deficiencies of even one of the amino acids can have grave consequences.

For example:Arginine deficiency causes a build up of ammonia in the bloodstream, causing vomiting in dogs and death in cats.Methionine and Cysteine deficiencies cause weight loss and skin disordersTaurine deficiency in cats leads to blindness and heart failure.

This information is found on page 298

Felines

• Cats are specifically adapted for a high protein, low carb diet. They depend on gluconeogenesis as a major source of energy. Cat’s are limited in their ability to conserve protein due to continuous protein catabolism.

• Dietary excess of protein is converted to fat and stored as adipose tissue. Metabolism of excess amino acids increases liver and kidney overload.

Cont. Felines

• Due to the dependency on gluconeogenesis, the feline has very little energy in reserve. If a cat becomes anorexic for any period of time, the body has little or no protein to breakdown for energy. Instead it breaks down fat. The fat accumulates in the liver causing acute liver failure, a condition called hepatic lipidosis (fatty liver disease).

Crude Protein

• Crude protein is only an estimate of the protein contained. It is obtained by measuring the amount of nitrogen.

• On average protein contains 16% nitrogen.

• To calculate the estimated protein, we must first mathematically removed the water

• This information can be found on page 312.

Case Study:

Pet food A has 8% crude protein and is a canned foodPet food B has 25% protein and is kibble

Which has the higher protein percentage??

First… we must remove the moisture..

The canned food is 75% moisture.100 – 75 = 25% dry matter

The kibble is 10% moisture.100 – 10 = 90% dry matter

Now you take the % of crude protein, divide it by the dry matter percentage and multiple by 100 to give you a percentage.

Canned food:8% CP / 25% DM x 100 = 32% estimated protein

Kibble:25% CP / 90% DM x 100 = 28% estimated protein

*remember, crude protein is a measurement of the nitrogen, therefore it is only an estimation of the total amount of actual protein.

Protein Requirements

• Unfortunately, the essential-to-nonessential amino acid profile, protein digestibility, and amino acid bioavailability may or may not be measured or stated on pet food labels.

• It is best to contact the manufacturer directly to obtain this information.

• Lower quantities of a higher biologic quality protein usually represent a higher quality food, and thus, a more appropriate nutritional objective.