I. Classification of protein

1, muscle part: muscle protein, actin.

2. Skin part: collagen

3. Milk secretion: casein and whey protein.

4. Blood composition: hemoglobin

5. Body fluids and digestive juices: enzymes

6. Hormones: insulin and glucagon

7. Hair: keratin

Second, the demand of dogs and cats for protein.

Malnutrition of cats and dogs in protein will lead to symptoms such as slow growth, stunting, emaciation, too little muscle mass, poor physical strength and impaired reproduction.

1, Newborn dogs and cats:

Newborn cats and dogs need nutrition from breast milk. The main nutrients in breast milk are protein, lactose, fat, calcium, magnesium, iron, zinc and copper.

The protein content in the bitch's milk can reach more than 10% on the first day after delivery, and the protein content in the milk will gradually decrease in the next three weeks. The ratio of casein to whey protein in dog milk is about 7:3, and the value is relatively stable.

The content of protein in cat's milk is usually above 8% on the first day after delivery, and it will rapidly drop to about 4% within three days, and then it will slowly return to about 8%. The ratio of casein to whey protein in cat milk will gradually change from 4:6 to 6:4.

2. Weaned dogs and cats:

According to the dog food standard of AAFCO (American Animal Food Management Association), the content of protein in the dog food eaten by puppies and breeding dogs should reach at least 22.5%, and the minimum content of protein in adult dog food is 18%.

In the diets of young cats and breeding cats, the content of protein should reach at least 30%, and the minimum content of protein in adult cat food should reach 26%.

Because old dogs and cats will lose protein in the process of aging, and the storage of protein in their bodies will be reduced, they should also be fed pet food with a higher level in protein.

3. Essential amino acids for dogs and cats

The basic unit of protein is amino acid, which can be obtained by hydrolysis of protein.

Protein hydrolysis process: protein → polypeptide → small peptide → amino acid.

1, amino acid type

Amino acids are divided into essential amino acids and non-essential amino acids.

There are 10 kinds of essential amino acids: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine and taurine. Taurine is only an essential amino acid for cats.

Nonessential amino acids include alanine, aspartic acid, asparagine, cysteine, glutamic acid, glutamine, glycine, serine, tyrosine and proline.

2. Amino acid balance

When protein is synthesized by amino acids in animals, the utilization rate of amino acids will be higher if the amino acid content of each group is close to the proportion required by the body. If the amino acid content is too high, it will be converted into energy or stored as body fat.

The demand ratio of amino acids is determined according to the physiological needs of animals, so the content of amino acids in pet food is not as high as possible.

3. Antagonism of amino acids

The principle that the existence of one amino acid causes the absorption and utilization rate of another amino acid to decrease is called amino acid antagonism.

The following amino acids are antagonistic:

Basic amino acids: arginine, lysine and histidine.

Acidic amino acids: aspartic acid, glutamic acid

Branched-chain amino acids: leucine, isoleucine and valine.

Aromatic amino acids: tyrosine, phenylalanine, tryptophan

For example, supplementing lysine to cats can antagonize arginine, an amino acid that can promote the synthesis of herpes virus.

4. Important amino acids for dogs and cats

Arginine: Dogs and cats of all ages can't lack arginine. Lack of arginine can lead to hyperammonemia in cats and dogs. Clinical symptoms mainly include vomiting, limb spasm, muscle tremor and so on. In severe cases, it can lead to coma and death.

Lysine: This is the first restricted amino acid in cereal dog food. Dogs and cats lacking lysine will have symptoms of growth stagnation, weight loss and weak resistance.

Methionine and cysteine: Methionine is an essential amino acid, and cysteine is a non-essential amino acid. In most pet foods containing animal protein and plant protein, methionine is usually the first restrictive amino acid, and some methionine will synthesize cysteine.

Taurine: Taurine is a free amino acid that does not participate in the synthesis of protein, but it is an essential amino acid for cats' physical condition. Cats can only synthesize a small amount of taurine. Wild cats will supplement taurine by hunting animals such as mice, while domestic cats can only get it through diet. Taurine deficiency can lead to retinopathy in cats and easily lead to dilated cardiomyopathy.

Through the above contents, we can understand the nutritional needs of dogs and cats of different ages for protein, and some essential amino acids in the diet of dogs and cats, which can help us to select more qualified and high-quality pet food and make pets eat more nutritious and healthy. If you have other questions about pet keeping, you can always consult an online pet doctor.