Sources, Functions And Requirements | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Sources, Functions, and Requirements of Vitamins

Vitamins

Vitamins are essential organic compounds required in small amounts for the proper growth and functioning of animals. They are classified into fat-soluble (A, D, E, and K) and water-soluble (B-complex and C) vitamins.

• Discovery and Importance of Vitamins: The concept of vitamins emerged in the early 20th century when researchers observed that certain diseases like scurvy and beriberi could be prevented by including specific food substances in the diet.
• Classification of Vitamins: Vitamins are categorized into fat-soluble and water-soluble groups. Fat-soluble vitamins are stored in the body, while water-soluble vitamins need to be consumed regularly.
• Animal Vitamin Requirements: Animals have varying requirements for vitamins, and these are often expressed in different units based on their diet, energy intake, or body weight. Some vitamins can be synthesized by the animal itself, while others need to be supplemented.
• Commercial Considerations: Vitamins are sensitive compounds that can be easily destroyed by factors like oxidation, heat, and light. Commercially available vitamin supplements often claim to provide stabilized forms of vitamins for animal consumption.
• Vitamin Deficiency: Inadequate intake of vitamins can lead to deficiency diseases in both humans and animals. Factors like poverty, dietary restrictions, and medical conditions can contribute to vitamin deficiencies.
• Human and Animal Vitamin Synthesis: While some animals can synthesize certain vitamins internally, others rely on external sources for their vitamin intake. Understanding the synthesis capabilities of animals helps in formulating appropriate diets.

Fat-Soluble Vitamins

Vitamin A:

• Vitamin A, also known as retinol, is crucial for animals.
• It plays a vital role in maintaining eye health, preventing night blindness (nyctalopia), and sustaining the integrity of epithelial cells.
• Vitamin A exists in different forms like retinal and retinoic acid.
• It is primarily sourced from animal tissues, with the liver being the richest source, especially in marine fish liver oils.
• Provitamin A sources include carotene, found in plants like carrots, spinach, and sweet potatoes.

Metabolic Role: Digestion, Absorption, Transport, and Storage

• Vitamin A and carotenoids are absorbed in the small intestine, influenced by dietary fat and emulsifying agents.
• In some animals, like horses and cattle, carotene is partly converted into vitamin A and stored in the liver and adipose tissue.
• After absorption, vitamin A is transported via the lymph system to the liver, stored as an ester, and released into the bloodstream as needed.

Physiological Functions of Vitamin A

• Vitamin A plays key roles in vision, bone growth, maintenance of mucus-secreting cells of epithelia, and reproduction.

Vision:

• Vitamin A is essential for the formation of rhodopsin, necessary for vision in dim light.
• Rhodopsin is formed from 11-cis-retinal and Scotopsin in darkness, crucial for vision in low light conditions.

Bone Growth:

• Vitamin A regulates the activity of bone-forming and bone-destroying cells, affecting bone health.
• Deficiency can lead to bone abnormalities in various species.

Maintenance of Mucus Secreting Cells of Epithelia:

• Vitamin A influences the differentiation of epithelial cells, crucial for mucus secretion.
• It affects various epithelial tissues differently based on their threshold to vitamin A effects.

Reproduction:

• Vitamin A deficiency can impact reproduction, separate from its effects on vision and bone development.
• Studies have shown restored reproductive functions in animals with vitamin A supplementation.

Deficiency and Toxicity of Vitamin A:

• Vitamin A deficiency symptoms include loss of appetite, poor growth, bone abnormalities, and vision issues.
• Toxicity symptoms may include decreased appetite, bone issues, and increased intracranial pressure.
• Excessive vitamin A intake can lead to hypervitaminosis, causing various health problems.

Physiological Functions of Vitamin D:

• Vitamin D is essential for calcium and phosphorus metabolism, bone health, and overall growth.
• Deficiency can lead to conditions like rickets and osteomalacia in animals and humans.
• Vitamin D sources include sun exposure, fortified foods, and supplements.
• Excessive vitamin D intake can result in toxicity, leading to hypercalcemia and other complications.

Additional Information on Vitamin E:

• Vitamin E deficiency was initially linked to reproductive issues in rats but is now known to have diverse effects across species.
• The role of vitamin E in reproductive health varies among different animal species.

Metabolism of Vitamin D

Digestion and Transport in the Body:

• Vitamin D is primarily absorbed in the lower part of the small intestine, specifically in the jejunum and ileum, in the form of fat micelles.
• It is transported through the lymphatic system to the thoracic duct in most mammals, where chylomicrons and lipoproteins containing vitamin D are released into the bloodstream.
• Vitamin D plays a crucial role in the absorption of calcium and phosphorus in the intestine.
• It is active in regulating the synthesis of RNA necessary for calcium-transporting proteins, aiding in the transfer of calcium across cell membranes.
• Hydroxylated vitamin D (25(OH)D) from the liver travels to the kidney, where it undergoes further hydroxylation to form 1,25(OH)2D, which acts as a steroid hormone mediating calcium transport in the intestine and bone.
• Parathyroid hormone-induced mobilization of bone mineral is dependent on the presence of vitamin D.

Distribution and Storage:

• Within four hours of injection, vitamin D is distributed widely in all tissues, with the highest concentrations found in the bone, liver, blood, and kidneys.
• The exact storage site of vitamin D is still unknown.
• Excess vitamin D is catabolized into various derivatives and excreted into the small intestine.

Vitamin E Metabolism:

• Vitamin E occurs naturally in plant materials as tocopherols and tocotrienols.
• Chicks metabolize D2 more rapidly than D3, making D2 more effective.
• Various forms of vitamin E exist, with tocopherol being the most biologically potent.

Role and Sources of Vitamin E:

• Vitamin E deficiency can lead to degenerative muscle changes similar to muscular dystrophy.
• Selenium is essential for animals and can prevent or cure diseases caused by vitamin E deficiency.
• Initial sources of vitamin E were detected in lettuce leaves and oils extracted from plants like green feeds and cereal grains.

Metabolic Role of Vitamin E:

• Vitamin E is assumed to be absorbed during fat digestion as part of micelles due to its fat-soluble nature.
• When provided in acetate form, it is hydrolyzed in the small intestine before absorption, with additional amounts hydrolyzed in the intestinal mucosa and distributed throughout the body.
• Vitamin E appears in the bloodstream in the form of tocopherol bound to lipoproteins.

Vitamin E:

• Vitamin E is essential for metabolic systems as a biological antioxidant and plays a crucial role in biological oxidation-reduction reactions involving cytochrome e reductase and the succinate oxidase system.
• It is involved in DNA biosynthesis and its regulation within the cell.
• Vitamin E is closely related to sulfur, amino acid metabolism, the synthesis of ubiquinone, phosphorylation reactions, as well as selenium and vitamin A metabolism.
• The exact role of vitamin E remains a mystery in biochemical reactions in animals.
• Deficiency of Vitamin E leads to diverse symptoms, with blood clotting time being a significant indicator.
• Newborn babies, especially premature infants, may require a supplemental source of vitamin E.
• Ruminants can compensate for the deficiency of vitamin K by synthesizing other substances like sulfur, amino acids, selenium, and antioxidants.

Vitamin K:

• Vitamin K was discovered by Henrik Dam, who found that chickens fed on low-fat diets exhibited hemorrhages and prolonged blood clotting time.
• Vitamin K is essential for the biosynthesis of plasmatic factors and acts as a coenzyme or prosthetic group in necessary enzymes.
• Deficiency in animals leads to decreased synthesis of prothrombin and prolonged clotting time.
• Vitamin K deficiency is commonly observed in poultry and rarely in humans and cattle, with dicoumarol poisoning occurring in cases of severe deficiency.

Water Soluble Vitamins

• All vitamins of the B group are essential for monogastric animals, which cannot produce most of them except niacin and choline.
• Ruminants can synthesize all B vitamins with the help of microbes in their rumen.
• Thiamine (Vitamin B1) is crucial for energy metabolism and nerve function.
• In deficiency, thiamine can lead to conditions like accumulation of pyruvic acid in cattle.

Thiamine (Vitamin B1)

• Comprises a pyrimidine molecule joined to a thiazole ring.
• Plays a role in phosphorylation and coenzyme formation in the presence of ATP.
• Deficiency can result in diseases like haemorrhagic sweet clover disease in cattle.
• Administration of vitamin K can counteract the effects of dicoumarol.

Riboflavin (Vitamin B2)

• Made up of ribose and isoalloxazine, it is more heat stable than thiamine.
• Acts as a component of flavoproteins essential for hydrogen transport in the body.
• Excess riboflavin is excreted in urine, giving it a yellow color.

Metabolism of Riboflavin

• Optimal absorption is aided by bile in the intestine.
• High levels of vitamin A can interfere with riboflavin absorption.
• Deficiency can lead to conditions like curled toe paralysis in chicks.

Vitamin K: 

• Essential for blood clotting and bone health.
• Found in high concentrations in green leafy vegetables and certain meats.
• Deficiency can result in clotting disorders and bone abnormalities.

Sources of Vitamin K

• Cereal grains and by-products are rich sources of vitamin K.
• Green leafy vegetables like spinach and kale are excellent sources for humans.

Vitamins and Their Functions

• Niacin, a water-soluble derivative of pyridine, exists as nicotinamide, the amide form of nicotinic acid.
• It is a component of coenzymes I and II crucial for oxidation-reduction reactions by accepting hydrogen atoms from substrates and transferring them to other molecules.
• Deficiency in niacin leads to pellagra, a disease characterized by symptoms like mouth inflammation, skin redness upon light exposure, dermal lesions, and intestinal inflammation.
• Supplementation is necessary in high-energy diets of rapidly growing animals like chicks and turkeys.

Pyridoxine (Vitamin B6):

• Pyridoxine, the biologically active form of vitamin B6, is vital for various enzyme systems, including amino acid metabolism.
• Its deficiency results in reduced growth in birds, decreased egg production, and anemia in pigs.
• Food sources of pyridoxine include whole grains, leafy vegetables, muscles, and liver.

Pantothenic Acid (Vitamin B5):

• Pantothenic acid, a dipeptide derivative, serves as a component of coenzyme A, aiding in the transfer of acyl groups.

Folic Acid:

• Folic acid, composed of glutamic acid, para-aminobenzoic acid, and pteridine, is essential for single-carbon unit transfer in various enzyme systems.
• It plays a crucial role in purine and pyrimidine synthesis, impacting macrocytic anemia and growth rates.

Biotin (Vitamin B7):

• Biotin, a sulfur-containing vitamin, is involved in carbon dioxide activation and amino acid metabolism.
• Deficiency in biotin can lead to dermatitis, slow growth, and perosis in animals like swine and poultry.
• Food sources rich in biotin include yeast, rice bran, liver, and corn.

Choline:

• Choline, classified as a vitamin, is crucial for structural compounds like phospholipids and nerve impulse transmission.
• It is synthesized by most animal species, with higher concentrations required in certain animals like chickens and guinea pigs.
• Deficiency in choline may lead to various symptoms like slow growth, perosis, and nerve issues.

Vitamin B12:

• Vitamin B12, also known as cyanocobalamin, is essential for red blood cell formation and nervous system health.
• Its deficiency can cause macrocytic anemia, leukopenia, and nerve degeneration in humans and animals.
• Sources of vitamin B12 include animal products, liver, and cereal grains.