Role of Vitamin D Metabolites in Animal Nutrition

The history of Vitamin D in animal nutrition dates back to the early 20th century when a disease, now called rickets, used to be treated with cod liver oil. In 1924 Steenbock demonstrated that antirachitic activity could be generated by irradiation of foods with ultra-violet light. The antirachitic component was named Vitamin D by McCollum in 1925.


Further studies in animal nutrition of Steenbock et al. and Bethke et al. showed the inability of fowl to utilize irradiated ergosterol from plant sources as effectively as cholecalciferol from fish oils. It was found that Vitamin D in synthesis in plants is chemically different from its synthesis in animal bodies.




Vitamin D in animal nutrition is also known as the "Sunshine Vitamin: as when skin is exposed to ample sunlight, Vitamin D is synthesized by different molecules. Cholecalciferol (Vitamin D.). (occuring in animals) and Ergocalciferol (Vitamin D.). (occurring in plants) are the two main natural sources of Vitamin D in animal nutrition. As such Vitamin D  would mean either Vitamin D, or Vitamin D, in the absence of a subscript.

Physiologically Vitamin D in animal nutrition, metabolites 25 (OH) D₁, 1-a-(OH) D, and 1, 25 (OH), D, are more effective than Cholecalciferol because all the Cholecalciferol entering the system is not converted into active metabolites. Active metabolites may directly reach the target tissue by bypassing hydroxylation in liver and kidney, hence have more efficacy than Vitamin D, (Goodgame et al., 2011).


In animal nutrition when given through diet like all fat soluble vitamins, Vitamin D in is absorbed from the digestive tract. Like the others, it requires the presence of bile salts for absorption (Braun, 1986), and is absorbed through chylomicron into the lymphatic system of animals along with other lipids.


Sunlight and Vitamin D in animal nutrition


The 7-dehydrocholesterol present in the skin is converted into Vitamin D, by irradiation. Ultraviolet light of 230 to 320 nm wavelength affects the conversion by imparting a definite quantity of energy to the sterol molecule.

Chemical Nature


Vitamin D  comprises a group of compounds with antirachitic activity that are closely related. It can be administered through the diet or through irradiation in animal nutrition. There are around 10 pro-vitamins with variable antirachitic activity after irradiation. Ergocalciferol (Vitamin D₂) and cholecalciferol (Vitamin D.) are the two most effective compounds of this group.


In animal nutrition The term D, was originally suggested for activated sterol, which was later found to be impure and consisted primarily of ergocalciferol, which had already been termed as Vitamin D The result of this confusion was that the term Vitamin D, was abolished in the D vitamin group. The D vitamins are insoluble in water but soluble in fats and fat solvents. Vitamin D , and Vitamin D, are both more oxidation-resistant than Vitamin A, whilst Vitamin D in, is more stable than Vitamin D₂.




Dietary Vitamins D₂ (Ergocalciferol) and D, (Cholecalciferol) are absorbed from the small intestine and are transported by the blood to the liver, where they are converted into 25 hydroxycholecalciferol.


In animal nutrition The vitamin, whether intestinally absorbed or produced in the skin, is hydroxylated primarily in the liver by 25-hydroxylase to form 25 hydroxycholecalciferol (25-OH- D.). If elevations in parathyroid hormone signal a need for increased circulating calcium levels, 25-OH-D₂-1 hydroxylase hydroxylates 25-OH-D, on carbon 1 to produce 1,25-dihydroxy Vitamin D, (1,25-(OH), D₂).






Supplemental Forms of Vitamin D


Vitamin D is an essential nutrient with a major role in the regulation of a number of genes, many of which are involved in calcium absorption and transport along with cell development. Vitamin D for animal nutrition is normally supplemented as cholecalciferol. This form has to be hydroxylated first in the liver as 25-hydroxy-cholecalciferol and subsequently, in the kidney as 1,25-dihydroxy- cholecalciferol. This dihydroxy compound is the main metabolically active form of Vitamin D and binds to the Vitamin D receptor (VDR) which then binds to the Vitamin D in animal nutrition response element in genes.


Vitamin D in animal nutrition


The role of Vitamin D in animal nutrition, and in supporting production is well established. Vitamin D, is the most important molecule for calcium absorption in the intestine.


In animal nutrition Vitamin D. (Cholecalciferol) is available either by the conversion of 7-dehydrocholesterol to cholecalciferol in the skin or from dietary sources. In modern animal nutrition production where animals are kept in farms, the conversion of 7 dehydrocholesterol to cholecalciferol does not ensure enough cholecalciferol. Hence, Vitamin D in is regularly supplemented in  through premixes in animal nutrition.


25-Hydroxy Vitamin D


This metabolite is synthesized by hydroxylation of cholecalciferol in the liver.


1,25-Dihydroxy Vitamin D



DeLuca (1974) concluded on the basis of many experiments with 1,25(OH)₂D, that 1,25(OH), D₁ is a steroid hormone and is a biologically active Vitamin D metabolite in animal nutrition. It is ten times more effective in ricket prevention and cure than Vitamin D,.


Glycoside form of 1,25-dihydroxy Vitamin D


1,25-dihydroxy Vitamin D, glycoside is of plant origin and is derived from the waxy-leaf nightshade (Solanumglaucophyllum). This plant naturally contains 1,25 (OH), D, the metabolically active form of Vitamin D in a glycosidic form. Several studies with different animal species have proved its role in correcting problems associated with Vitamin D deficiency in animal nutrition. The heat stability of the glycoside form is preferred over other metabolic forms of Vitamin D, hence making it ideal for on top as animal nutrition supplement.

Role of Vitamin D in supporting immunity in animal nutrition


When pathogens invade the body, the immune system first activates the innate and then the acquired host defense systems. Antimicrobial defences of the macrophages depend on the 10 hydroxylase activity in the macrophages and the availability of Vitamin D for animal nutrition. If Vitamin D is insufficient, the immune system is compromised, and the animal is at greater risk of infectious diseases.


1a-hydroxylase activity in immune cells produces 1,25 dihydroxycholecalciferol which triggers innate defenses of the immune system by stimulating production of defense proteins that kill pathogens. When there is a deficiency of Vitamin D, immune system function may be impaired even if the animal does not exhibit symptoms of conventional Vitamin D deficiency in animal nutrition.


Deficiency Symptoms


In animal nutrition Vitamin D deficiency in causes Osteomalacia in older animals, in which bone reabsorption has already developed. Osteomalacia arising out of Vitamin D deficiency is not normal in farm animals, although pregnant and lactating animals that need increased amounts of calcium and phosphorus may experience a similar condition. Rickets and Osteomalacia are not particular disorders that are exclusively caused by Vitamin D deficiency but they may also be caused by a lack of or an imbalance of calcium and phosphorus.

In Poultry


In poultry, Vitamin D deficiency in causes the bones and the beak to become soft and rubbery. It also is the cause for retarded growth and leg weaknesses. Egg production can reduce and eggshell quality may deteriorate. Poultry feeds with the exception of fishmeal, contain little or no Vitamin D.This vitamin is generally supplied in the form of fish-liver oils or synthetic preparations.

Tibial dyschondroplasia (TD) is one of the most common skeletal abnormalities observed due to Vitamin D deficiency in poultry. TD represents deformed bones and lameness in birds. It is a disease common in rapidly growing birds, especially broilers and turkeys. Comparisons between fast growing and slow-growing strains have revealed less mineralization and more porous cortical bone in fast growing birds.

Vitamin D supplementation in animal nutrition of breeder birds impacts its content in egg yolks. Deficiency leads to marked reduction in hatchability and frequent mortality of embryos. These embryos show a short upper mandible or incomplete formation at the base of the beak.


In Ruminants


In animal nutrition Clinical signs of Vitamin D deficiency in ruminants are decreased appetite, decreased growth rate, digestive disturbances, stiffness in gait, labored breathing, irritability, weakness, and occasionally tetany and convulsions. There is an enlargement of joints, slight arching of the back, and bowing of legs, with an erosion of joint surfaces causing difficulty in locomotion. Sometimes, young ruminants may be born weak, deformed or dead.


Milk fever (parturient paresis) is a paralyzing metabolic disease caused by hypocalcemia near parturition and initiation of lactation in high milk- producing dairy cows. Milk fever is an impaired metabolic condition that is related to Ca status, historical Ca intake, and malfunction of the hormone form of Vitamin D in  [1,25-(OH),D.] and the Parathyroid hormone PTH. Animals that develop milk fever are unable to meet the sudden demand for Ca that is brought about by the initiation of lactation.



In Swine


In swine, Vitamin D deficiency  causes poor growth, stiffness, lameness, stilted gait, posterior paralysis, fractures, softness of bones, bone deformities, beading of the ribs and enlargement of joints. Bones may get deformed by the weight of the animal and the pull of body muscles.




Fast growing and high performing birds and animals frequently experience bone and health challenges due to poor absorption or imbalance or deficiency of Calcium and Phosphorus, all of which lead to reduced performance. In the modern animal farming industry, where the birds and animals are mostly raised indoors, adequate availability of Vitamin D in animal nutrition is essential to ensure proper turnover of calcium and phosphorus in the body.


In practice, deficiency of Vitamin D in animal nutrition is quite common and leads to several performance related issues. While regular supplementation of Vitamin D, through premixes is common, there are more bioactive forms of this vitamin which do not require liver and kidney level conversions. Often, due to disease conditions, the liver and kidney do not work efficiently which adversely affects the conversion of Vitamin D  into its active form. To meet such challenges, in the field of animal nutrition a biologically active form of Vitamin D represents an answer in managing the gap between Vitamin D requirement and availability.