Originally Posted by pstinard  Hi,
In another thread on dog food and canine nutrition, the question came up about whether menadione (vitamin K3) is necessary in dog food, and if it is, whether it is a safe ingredient. There are many, many articles about it in the popular press, but they tend to go around in circles, and don't cite any scientific articles to back it up. For that reason, I'm not going to post any articles from the popular press on this subject, not even from the Skeptvet. I'm going to try to find the facts about menadione. First, here is the section on vitamin K from a chapter from the book "Canine and Feline Nutrition. A Resource for Companion Animal Professionals, Third Edition" by Case, LP, Daristotle, L, Hayek, M, and Raasch, MF. 2011. Mosby Elsevier Press, Maryland Heights, Missouri.
Vitamin K
Vitamin K comprises a group of compounds called the quinones. Vitamin K1 (phylloquinone) occurs naturally in green plants, and vitamin K2 (menaquinone) is synthesized by bacteria in the large intestine. Several synthetic analogues have also been prepared. Menadione (vitamin K3), the most common form of synthetic vitamin K, has a vitamin activity two to three times higher than that of natural K1. Like all animals, dogs and cats have a metabolic need for vitamin K. However, at least a portion of this requirement can be obtained from bacterial synthesis of the vitamin in the intestine.
The best-known function of vitamin K is its role in the blood clotting mechanism. Specifically, it is required for the liver's synthesis of prothrombin (factor II) and three other clotting factors--factors VII, IX, and X--in the liver. Vitamin K acts as a cofactor for the enzyme that carboxylates glutamic acid residues in a prothrombin-precursor protein to form gamma-carboxyglutamic acid. The conversion of these amino acids facilitates the binding of prothrombin to calcium and phospholipids., a process necessary for the occurrence of normal blood clotting. It appears that vitamin K has a similar role in the activation of other proteins that contain glutamic acid residues in bone and kidney tissue.
Vitamin K is found in green, leafy plants such as spinach, kale, cabbage, and cauliflower. In general, animal sources contain lower amounts of vitamin K; liver, egg, and certain fish meals are fairly good sources. The synthesis of vitamin K by bacteria in the large intestine of dogs and cats can contribute at least a portion, if not all, of the daily requirement in these species. Therefore a dietary supply of this vitamin only becomes significant when bacterial populations in the large intestine are reduced, such as during medical treatment with certain types of antibiotics, or when there is interference with the absorption or use of vitamin K from bacterial sources. Vitamin K is also routinely administered in the treatment of rodenticide poisoning in pets because the active ingredient in many of these poisons is an anticoagulant. |