Cobalt is an important active component of the structure of vitamin B12 (cobalamin, VB12). It has a unique position in ruminant nutrition and is the only essential trace element for vitamin essential component (VB12). The absorption rate of cobalt in animals is not high, and the absorption of soluble cobalt by ruminants is worse than that of non-ruminants. The lack of cobalt in the diet, the ability of microbial synthesis of VB12 is limited, resulting in the lack of VB12 in ruminant livestock, directly affecting the animal's production performance. Therefore, its nutritional role has increasingly attracted people's attention.
metabolism in ruminant
1.1 Cobalt absorption, metabolism
Cobalt is produced in small amounts in animals. Most of it enters the body with feed or feed additives. The metabolism of cobalt in ruminants is mainly in the rumen. What ruminants need is not cobalt itself, but VB12 synthesized by rumen microbes using cobalt. A large amount of VB12 can be synthesized in the rumen, but only a part of it has VB12 activity, and the rest is a VB12 analog which does not have any physiological function to the animal, so the amount of cobalt added in the ruminant diet is relatively high.
Ruminants mainly absorb cobalt in the small intestine. About 3% of the cobalt absorbed from the diet is used for rumen microbes to synthesize VB12 required by ruminants, and VB12 can only be absorbed by combining with gastric mucosal proteins, so the absorption rate is very low. The rest are absorbed by the intestinal tract in the form of cobalt-protein complexes and inorganic salts, and then enter the bloodstream to bind to cobalt-cobalt protein, which enters the liver through the portal vein and is then transported to the whole body.
1.2 Cobalt excretion
Most of the absorbed cobalt is excreted from the body. The excretion of different animals is different. The cobalt excreted by the lactating cows with the feces accounts for 86%-87.5% of the total excretion, and the cobalt excreted with the milk accounts for 11.5%-12.5%, which is discharged with the urine. Cobalt accounts for 0.9%-1.0%. During the dry period, the cobalt excreted by the cows accounts for 98%-98.5% of the total discharge, and the cobalt excreted with the urine accounts for 1.5%-2.0%. Animals take different ways of taking cobalt, and their excretion methods are also different. This difference may be related to the chemical form of cobalt.
in the role of ruminant nutrition
The nutrient metabolism of cobalt in the body is essentially the metabolism of VB12. Cobalt exerts its biological function mainly in the body by forming VB12. Ruminants require more cobalt or VB12 than monogastric animals. Cobalt will have an impact on the metabolism of substances in animals, the growth and reproduction of animals, and immunity.
2.1 The impact on the synthesis of VB12
Cobalt participates in the construction of specific structures of VB12 in living tissues. When the cobalt content in the diet reaches 0.3 mg·kg -1 or more, the synthesis of VB12 can be promoted; when the cobalt intake is insufficient, the synthesis of VB12 is reduced. The synthesis and metabolism of VB12 in high-yield ruminants is directly dependent on the amount of cobalt in the diet. He Ruiguo et al. added different amounts of cobalt to goat diets to study the effects of different cobalt additions on the synthesis of rumen VB12 in goats. The results showed that the content of VB12 in rumen fluid and serum increased with the increase of cobalt in the diet. Thus, it was confirmed that the amount of inorganic cobalt added in a certain range of the diet has a high correlation with the VB12 content in the rumen fluid and serum. Studies have shown that with the increase of cobalt in the diet, the synthesis of VB12 also increases, and the absorption of VB12 is consistent with its synthesis. Hou Shengzhen et al. added cobalt and VB12 to the yak diet of Holstein bulls and primiparous Qinchuan cows. The results showed that the addition of VB12 to yak diet was beneficial to the growth and development of yak. The addition of cobalt to the yak diet not only contributes to the increase in the amount of rumen microbial synthesis of VB12, but also plays a unique nutrient metabolism of cobalt. It is recommended to add cobalt and VB12 to the yak diet at the same time.
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