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What is the interest of collagen?

Collagen is a protein of fibrillar structure. It is one of the major components of numerous tissues: subcutaneous connective tissue, tendons, aponeurosis, articular capsules, cartilages, osseous matrix… The level of collagen in the meat can be estimated through the importance of the white “ fibers ” that can be seen. On the contrary, fish are very poor in collagen, as they do not have much connective tissue.

Digestion of collagen

Raw collagen arrives undigested in the large intestine. Then, it becomes a substrate for bacterial fermentation that produces a range of undesirable products such as: ammonia, hydrogen sulphide, biogenic amines (histamine, cadaverine, putrescine…), that:

  • encourage the production of very foul-smelling stools, loose and watery,
  • can be toxic and promote digestive or cutaneous diseases.

When a dog is fed a traditional diet, very rich in collagen (based upon low quality meat byproducts, pork rind…), he is exposed to suffer from proteic maldigestion.

Cooking under high-pressurized water prevents from these inconvenients. Collagen is then transformed into gelatine, easily attacked by digestive enzymes. Properly cooked, collagen represents a source of amino-acids among others.

Nutritional value of collagen

The amino-acid composition of collagen is not good enough to meet all the requirements of carnivorous. Actually, it does not contain enough of tryptophane and lysine, that are two indispensable amino-acids. Here we speak about “ limiting factor ” or “ limiting amino-acids ”, because the body needs a optimum level in all the indispensable amino-acids to be able to synthetize its own proteins.

But other sources of proteins also have limiting factors; examples:

  • meats and soya proteins do not contain enough sulphurated amino-acids (methionine, cystine),
  • wheat is nutritionnaly deficient in lysine, etc…
Collagen cannot represent a single source of proteins. It can be utilized by dogs and cats, but provided that it is associated with other proteins that have different limiting factors, in order to make up for the tryptophane and the lysine deficiencies. Professor Wolter used to illustrate this fact by the image of two chains brought together, who contain some weak links. Once superimposed, they have a higher resistance than if they were considered individually.

Arginine Tryptophane Valine Lysine Leucine Methionine Cystéine

Dosage of collagen

Collagen is characterized by the presence of 2 specific amino-acids: hydroxylysine and overall hydroxyproline. Through the dosage of hydroxyproline, it is possible to calculate the approximate level of collagen in a meat:

% hydroxyproline x 7,2 = % collagen.

Examples of collagen ratio compared to total protein content in different dry petfood ingredients

protein’s sources % protein % collagen / total protein beef dehydrated protein (80) 80,0 42,8 beef dehydrated protein (65) 66,0 35,2 standard poultry meal 65,5 33,9 “ low ash ” poultry meal 70,0 31,6 dehydrated poultry meat 73,1 9,35 fish meal 69,5 3,9 egg powder 46 0 gluten of maize 60 0 soya 50 47 0

A low level or zero collagen does not mean that the protein is an excellent one. For example, lung or teats, that are very commonly used in canned food, contain very little collagen, but a lot of elastin, whose nutritional value is not better than the collagen one. On the other hand, vegetable proteins do not contain collagen but it does not mean that they are more interesting than animal meals as their digestibility is often lower.


Once cooked, collagen is a very interesting source of proteins, although incomplete. To compensate for its amino-acids deficiencies, it has to be mixed with other sources of proteins. So, the dosage of collagen cannot be used as a reference to judge the quality of a pet food.

Donated by the Borg Cardona and Co. Ltd. visit Borg Cardona website

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