What is "25-Hydroxyvitamin D3"?

25-Hydroxyvitamin D3, also known as 25-hydroxycholesterol, 25-hydroxycalciferol, or calcidiol, is medically referred to as calcitriol and abbreviated as 25-OH-D3.

In 1966, Lund and DeLuca discovered that after the administration of vitamin D, the vitamin itself disappears but several metabolites appear, which have stronger therapeutic activity against rickets.

The first metabolite is 25-hydroxyvitamin D3, which is found in the liver and is the circulating form of vitamin D in the body under normal conditions.

From a molecular structure perspective, 25-hydroxyvitamin D3 is formed by adding a hydroxyl group to the 25th carbon atom of vitamin D3.

However, this addition occurs through a series of biochemical reactions, where the enzyme 25-hydroxylase in the mitochondria of liver cells converts vitamin D3 into 25-hydroxyvitamin D3.

What are the differences between "25-Hydroxyvitamin D3" and regular vitamin D3?

(1) Vitamin D3 is a derivative of cholesterol and is only a precursor to its active metabolites in the body; it only has biological activity after being converted into 25-hydroxyvitamin D3.

(2) After absorption, vitamin D3 is stored in plasma, liver, fat, and muscle, and is then transported via the bloodstream to the liver for conversion into 25-hydroxyvitamin D3, where it is stored.

(3) Firstly, 25-hydroxyvitamin D3 is a derivative of vitamin D3.

Once hydroxylated, vitamin D3 gains a hydroxyl group, enhancing its water solubility and allowing it to circulate more easily in the blood, becoming the main circulating form. Normally, the concentration of 25-hydroxyvitamin D3 in serum is 3.1 times that of vitamin D3. Modern research indicates that the plasma level of 25-hydroxyvitamin D3 is a marker of the body's vitamin D3 nutritional status, but increasing dietary vitamin D3 levels cannot achieve the same effect.

(4) More importantly, the potency of 25-hydroxyvitamin D3 is 3 to 5 times that of D3, and its expressed biological activity is 20 to 40 times that of D3.

(5) 25-hydroxyvitamin D3 is absorbed more easily than D3, and it can be directly absorbed from the intestine (the interstitial cells of the small intestine) into the bloodstream, with absorption being less affected by intestinal damage, effectively increasing the level of 25-hydroxyvitamin D3 in the blood.

(6) The absorption rate of 25-hydroxyvitamin D3 is greater than that of pure vitamin D3; it can bypass liver conversion and enter the bloodstream more quickly and effectively. Research has reported that adding 25-hydroxyvitamin D3, compared to adding vitamin D3, increases its blood levels, improves calcium homeostasis, promotes bone and muscle development, and enhances immune response.

(7) The absorption method differs from that of fat-soluble vitamins (A, D3, E, K3), making it more efficient. Directly supplementing 25-hydroxyvitamin D3 shortens the metabolic process of D3 in the body, speeds up calcium absorption, and more effectively provides the traditional functions of D3 along with its unique benefits.

(8) It is not affected by liver dysfunction, avoiding issues related to impaired liver function in chicks due to underdeveloped livers, intestinal pathogens, drugs, and mycotoxins that can affect vitamin D3 absorption and conversion, thereby reducing the synthesis and metabolism of 25-hydroxyvitamin D3.

(9) 25-hydroxyvitamin D3 can regulate the intestinal mucosal structure in poultry, significantly enhancing the cumulative absorption effects in the gut. Studies have shown that using 25-hydroxyvitamin D3 can maintain optimal plasma levels even when the intestines of broilers are damaged, while regular vitamin D3 does not have such a pronounced effect.

(10) The half-life of vitamin D3 in poultry is about 25 days, while that of 25-hydroxyvitamin D3 is nearly 20 days. Therefore, directly supplementing 25-hydroxyvitamin D3, similar to vitamin D3, can ensure adequate vitamin D nutrition.

What are the effects of "25-Hydroxyvitamin D3"?

(1) In animals, 25-hydroxyvitamin D3 is more effectively absorbed and has higher biological activity than vitamin D3. Directly supplementing 25-hydroxyvitamin D3 not only shortens the metabolic process of vitamin D3 in the body, reducing the burden on the liver, but also avoids absorption issues due to intestinal damage or liver and kidney dysfunction.

(2) 25-hydroxyvitamin D3 is an important nutrient for maintaining bone health. It is more valuable than vitamin D3 in stimulating intestinal calcium absorption, regulating bone calcium, and promoting phosphorus absorption. Its significance in the production of laying hens, especially in bone development and eggshell quality, is extremely high. Adding 25-hydroxyvitamin D3 during the chick-rearing period can effectively prevent leg weakness, reducing chick mortality by 1-3%. Its effects are particularly notable during the growing phase for skeletal development and achieving shank length standards. During peak production, it reduces osteoporosis and cage fatigue in laying hens, increases egg production rates, and extends the laying period. In the late laying period, it increases eggshell thickness and strength, effectively preventing deformities, thin shells, and eggshell breakage, significantly improving eggshell quality and reducing breakage rates by 2%. It also noticeably improves issues like broken legs and wings due to calcium deficiency, helping maintain the weight of cull hens. For broiler chicks, good skeletal development leads to significantly higher meat yield, and increased bone density reduces the breakage rate during processing, maintaining good processing characteristics.

(3) Reports indicate that 2-week-old chicks cannot produce sufficient 25-hydroxyvitamin D3-25-hydroxylase. Therefore, when hatching chicks from breeding eggs sourced from hens fed low vitamin D3 diets, the chicks may exhibit rickets, and adding adequate vitamin D3 in the diet does not alleviate their symptoms. Conversely, when chicks come from hens on low vitamin D3 diets, adding 25-hydroxyvitamin D3 allows for normal growth, similar to chicks hatched from eggs with sufficient vitamin D3, even if they are given a vitamin D3-deficient diet during the first two weeks.

(4) High temperatures in summer can easily induce heat stress in chickens, adversely affecting growth rates, egg production rates, feed conversion rates, and mortality rates. The reduction in eggshell quality (thinning and brittleness) due to heat stress is related to decreased activity of the calcium carbonate enzyme in the hens' uterus and lower blood calcium levels. Production trials have demonstrated that supplementing 25-hydroxyvitamin D3 in hot environments leads to improved feeding outcomes, particularly in reducing mortality rates. Replacing 50% to 60% of vitamin D3 with 25-hydroxyvitamin D3 significantly increases weight gain and feed efficiency in broilers.

(5) When there is an imbalance of calcium and phosphorus in the feed, adding 25-hydroxyvitamin D3 can enhance their absorption. In the hot summer months, added phytase in the feed can become ineffective due to high temperatures, leading to insufficient bioavailable phosphorus and a calcium-phosphorus imbalance. In such situations, adding 25-hydroxyvitamin D3 is even more significant.

(6) 25-hydroxyvitamin D3 primarily regulates cellular immunity but also has strong regulatory effects on humoral immunity and antibody secretion. By modulating the immune system, it improves immune function and significantly enhances resistance to diseases.

(7) Effects on the reproductive performance of breeding poultry:

It significantly improves the production performance of breeding hens, reducing the incidence of cracked, white, and thin-shelled eggs, increasing the pass rate of breeding eggs, significantly improving hatchability, and maintaining high peak production rates while reducing embryonic mortality and achieving maximum bone capacity before sexual maturity, thus lowering early production mortality rates.

It effectively increases the semen volume and sperm count of breeding boars, improves the conception rate of sows, increases the number of live piglets in first-litter sows, enhances the immunity of nursing piglets, and improves survival rates. It also reduces feed costs, lowers acidity levels, and increases palatability.

(8) Effects on improving meat quality in poultry and livestock:

Research has found that due to the stimulatory effect of 25-hydroxyvitamin D3 on muscle calcium levels, the activity of proteases in muscle increases, thus improving water retention in meat, promoting tenderness and color improvement.

Additionally, for pigs and sheep, pre-slaughter supplementation with 25-hydroxyvitamin D3 can improve the color of pork, with subjective meat color ratings, firmness scores, and water-holding capacity increasing with higher intakes of 25-hydroxyvitamin D3.