Vitamins

Vitamins

Learning Objectives

  • Define vitamin and vitamin "terminology"

  • Classify vitamins as fat-soluble or water-soluble

  • Describe the functions of vitamins in general and specific to individual vitamins

  • List dietary sources of individual vitamins

  • Identify symptoms of specific vitamin deficiencies and toxicities

General Outline for Each Vitamin

  1. Description (classification, properties, structure, etc.)

  2. Physiological functions

  3. Dietary sources enriched in each vitamin

  4. Deficiency/toxicity symptoms

Animal Nutrition and the Vitamins

What is a Vitamin?

  • Operating definition:

    • A vitamin is an organic compound distinct from fats, carbohydrates, and proteins.

Characteristics of Vitamins

  • A vitamin is a natural component of foods where it is usually present in minute amounts.

    • Water (64%), Protein (20%), Fat (10%), Mineral (5%), Carbohydrate (0.95%)

    • Broiler body composition: Water (10%), Protein (56%), Carbohydrate (22%), Mineral (6%), Fat (5.5%), Vitamin (0.5%).

  • Essentiality:

    • A vitamin is not synthesized by the animal in amounts adequate to meet normal physiological needs.

    • It is essential (usually in minute amounts) for normal physiological function (i.e., maintenance, growth, development, production).

    • It causes (by its absence or under-utilization) a specific deficiency syndrome.

Caveats Related to Vitamins

  • Some compounds are vitamins for one species and not another (e.g., vitamin C and choline).

  • Some compounds are vitamins only under specific dietary or environmental conditions (e.g., vitamin D and niacin).

Definition of Vitamin-Related Terms

  • Vitamer:

    • Different chemical compounds that show the same biological activity (e.g., tocopherols and tocotrienols as forms of vitamin E).

  • Pro-vitamin:

    • A compound that can be metabolized to yield a vitamin (e.g., some carotenoids to vitamin A).

Importance of Vitamins

  • Coenzymes:

    • Catalysts in metabolism; most B vitamins serve in this role.

  • Antioxidants:

    • Prevent destruction of lipid membranes by free radicals (e.g., vitamins E and C).

Coenzyme vs. Cofactor

  • Coenzyme:

    • Small, organic non-protein molecule that carries chemical groups between enzymes to catalyze reactions.

  • Cofactor:

    • Non-protein, chemical element that is bound tightly to an enzyme and is required for catalysis.

  • Generally speaking, vitamins are coenzymes and minerals are cofactors.

General Classification of Vitamins

  • Fat-soluble:

    1. A

    2. D

    3. E

    4. K

  • Water-soluble:

    1. Thiamin (B1)

    2. Riboflavin (B2)

    3. Niacin (B3)

    4. Pantothenic acid

    5. Pyridoxine (B6)

    6. Biotin

    7. Folic acid

    8. Cobalamin (B12)

    9. C

Vitamin A

  • First vitamin discovered: 1913

  • Forms: Retinol (standard form)

Chemical Characteristics of Vitamin A

  • Represents a category of vitamers that differ in efficacy.

  • Found in free form or esterified with a fatty acid (e.g., retinyl palmitate).

  • Compounds with vitamin A activity, except carotenoids (carotenoids are pro-vitamins; >500 carotenoids in nature):

    1. Retinal (aldehyde form)

    2. Retinol (alcohol form)

    3. Retinoic acid (acidic form)

    4. Retinyl esters (esters of all-trans retinol).

Conversion Efficiency

  • Efficiency of converting $eta$-carotene to vitamin A varies by species.

    • 3.6% in milk fat.

    • 5.2% in milk fat.

    • Beta-carotene levels in milk are positively related to milk fat content.

    • Jersey and Guernsey breeds are less efficient at converting $eta$-carotene to vitamin A.

Vitamin A and Cats

  • Cats are not able to convert $eta$-carotene to active vitamin A.

  • Cats require pre-formed sources of vitamin A in their diet.

Chemical Properties

  • All forms of vitamin A are soluble in organic solvents and insoluble in water.

  • Unstable in the presence of oxygen, acids, and UV light.

Storage Time

Alfalfa Vitamin A Activity

Fresh

100%

Baled

42%

Six-month storage

11%

One-year storage

9%

International Units (IU)

  • Standardized measure of biological activity (or effect) of a compound.

  • Based on utilization of various forms by rats:

    • 1 IU of vitamin A activity = 0.300 µg retinol = 0.344 µg retinyl acetate = 0.550 µg retinyl palmitate.

    • On a mass basis, retinol has greater vitamin A activity than retinyl acetate or retinyl palmitate.

Functions of Vitamin A

  1. Vision:

    • Production of rhodopsin (pigment used in low light).

    • Required in rod cells of the eye; $ ext{11-cis retinal} + ext{opsin}
      ightarrow ext{rhodopsin}$ (+ light) $
      ightarrow ext{all-trans retinal} + ext{opsin}$.

    • Isomerization of $ ext{11-cis retinal}$ causes conformational changes in the protein and generates a nerve impulse to the brain.

  2. Maintenance of Mucous Membranes:

    • Soft tissue around the eye, digestive tract, respiratory tract, genitourinary tract, and corneal epithelium.

    • Maintains the epithelial lining throughout the body.

  3. Body Growth:

    • Required for growth and differentiation of cells, including proper bone growth (enlargement of the foramen for the optic nerve).

  4. Synthesis of Glycoproteins:

    • Essential for many physiological processes.

  5. Reproduction:

    • Required for reproductive function in both males and females; critical for hatchability of eggs.

  6. Corticosterone Synthesis:

    • Vitamin A deficiency causes atrophy of the adrenal gland, affecting the stress response.

  7. Immune Function:

    • Vitamin A deficiency reduces immune response.

Diverse Functions of Vitamin A

  • Gene Transcription:

    • Vitamin A plays a key role in gene transcription processes.

    • Retinoic acid receptors (RARs) serve as transcription factors that regulate gene expression, ultimately altering translation into protein.

  • As a fat-soluble vitamin, vitamin A can enter the nucleus and engage with transcriptional machinery within the cell.

Storage of Vitamin A

  • Vitamin A is primarily stored in:

    1. Liver

    2. Fat tissues (adipose)

  • Cattle can store a six-month supply when one million IU of vitamin A is administered via injection.

    • Supplementation required for cattle on winter range.

Natural Animal Sources of Vitamin A

  • Fish oils

  • Egg yolk

  • Liver

  • Butter

    • Yellow color due to $eta$-carotene!

Natural Vegetable Sources of Vitamin A

  • Kale

  • Carrots

  • Spinach

  • Pumpkin

  • Sweet potato

Grains and Vitamin A

  • Grains are low in vitamin A activity.

  • Yellow corn is the only grain with "significant" vitamin A activity, but on average, corn has only 10% the vitamin A activity of harvested alfalfa.

  • Total vitamin A requirements are usually achieved using vitamin supplements due to the cheap nature of vitamin A and the variability of feedstuffs concentration.

Vitamin A Deficiency

  • Vitamin A deficiency is an extremely common nutrient deficiency worldwide.

  • Deficiency Symptoms:

    • Night blindness

    • Xerophthalmia (inability to produce tears, dryness of the conjunctiva and cornea)

    • Keratinization of respiratory epithelium

    • Death

Vitamin A Toxicity

  • Hypervitaminosis A:

    • Ingestion of a large excess of vitamin A (>50 times above the metabolic requirement).

    • One of the few vitamins that can be toxic.

    • Gross Toxicity Signs:

    • Roughened hair coat

    • Scaly skin

    • Hyperirritability and sensitivity to touch

    • Blood in urine and feces

    • Loss of control of legs and inability to rise

    • Periodic tremors

Vitamin A Toxicosis in Cats

  • Most often reported in cats fed diets composed exclusively of liver or other organ meats.

  • Known as deforming cervical spondylosis, causing bony exostoses to develop along muscular insertions of cervical vertebrae and long bones of forelimbs.

Vitamin D

  • Exposure to sunlight/UV is a factor that contributes to the endogenous synthesis of vitamin D.

  • Most foods contain small amounts of vitamin D; fortification with vitamin D has become widespread in the food industry.

Forms of Vitamin D

  1. Ergocalciferol (D2): Plant form

  2. Cholecalciferol (D3): Animal form

Vitamin D Metabolism

  • Tightly regulated and tissue-specific metabolism; skin, liver, and kidney must all be involved for in vivo synthesis of active vitamin D.

Functions of Vitamin D

  • 1,25 (OH)2D3 (active vitamin D):

    • Intestine:

    • Induces synthesis of calcium-binding protein (required for active calcium uptake).

    • Stimulates intestinal transport of phosphorus and magnesium.

    • Bone:

    • Causes calcium mobilization.

    • Binds to a receptor, appears in nuclei of osteoblasts and osteocytes, mobilizes calcium (take up or release).

    • Kidney:

    • Involved in calcium conservation; however, sometimes it can increase calcium excretion.

    • Increases phosphorus resorption.

International Units (IU)

  • 1 IU of vitamin D activity is defined as:

    • Biological activity of 0.025 µg cholecalciferol.

  • Recommended Daily Allowance (RDA) for humans: 600 IU/day.

  • 1 cup of fortified milk contains approximately 125 IU vitamin D.

Vitamin D Source Importance

  • Vitamin D2 is equal to vitamin D3 in all species except poultry, which require D3 due to lesser metabolic capacity to synthesize the biologically active form.

Vitamin D Deficiency

  • Causes disturbance in absorption and metabolism of calcium and phosphorus, resulting in insufficient bone calcification.

  • It takes 4-6 months for young pigs fed a vitamin D-deficient diet to develop deficiency signs.

  • Deficiency Symptoms:

    • Rickets in young animals (soft bones)

    • Osteomalacia in adult animals (decreased mineral content and softening of bone)

    • Subclinical signs: reduced growth, milk production, egg production, reproductive performance.

Vitamin D Storage

  • Stored in the liver for a maximum of 3 months.

  • Metabolism is influenced by housing conditions and animal hair coat.

Natural Sources of Vitamin D

  • Liver

  • Fish oil

  • Alfalfa (sun-cured)

  • Mushrooms (UV-irradiated)

  • Egg yolk

Vitamin D Toxicity

  • Vitamin D is the most toxic of any vitamin.

  • Toxicity usually results from a formulation error.

  • Case study: Feeding 11,825 µg of vitamin D3 to young pigs resulted in death in 4 days (473,000 IU).

  • Daily upper intake for humans:

    • 4,000 IU.

  • Toxicity Symptoms/Effects:

    • Reduced feed intake (anorexia)

    • Reduced growth rate

    • Reduced liver weight

    • Excess calcium in blood (hypercalcemia)

    • Reduced weights of radius and ulna

    • Calcification of aorta, heart, kidney, and lung

    • Dehydration, vomiting, fatigue

Vitamin E

  • Includes tocopherols and tocotrienols.

  • Discovered in 1936 as a “dietary fertility factor in rats” ('toco' meaning "to carry a pregnancy").

  • Exists as light-yellow oils in pure form.

Chemical Forms of Vitamin E

  • Eight total forms (four tocopherols, four tocotrienols).

  • Most common form is DL-alpha-tocopherol.

Chemical Properties of Vitamin E

  • Vitamin E (DL-α-tocopherol).

  • Addition to feeds and foods acts as an antioxidant and protects against oxidation when in the presence of minerals and polyunsaturated fatty acids (PUFA).

  • If oils high in vitamin E are used, a synthetic antioxidant should also be included.

International Units of Vitamin E Activity

  • Definitions of activity:

    • 1 mg DL-α-tocopheryl acetate = 1.00 IU

    • 1 mg DL-α-tocopherol = 1.10 IU

    • 1 mg D-α-tocopheryl acetate = 1.36 IU

    • 1 mg D-α-tocopherol = 1.49 IU

  • Greatest potency per unit mass.

  • Unlike vitamins A and D, vitamin E IU conversions are especially sensitive to the exact vitamer/form being compared.

Functions of Vitamin E

  • Antioxidant:

    • Protection of vitamin A and prevention of oxidation of polyunsaturated fatty acids.

    • Interrelated with selenium; protects cell and mitochondrial lipid membranes from oxidative damage.

Vitamin E Deficiency

  • Nutritional muscular dystrophy (or cardiomyopathy); same deficiency signs as for selenium.

    • Deficiency Conditions Include:

    1. Mulberry heart disease (pigs)

    2. Stiff lamb disease (sheep)

    3. White muscle disease (calves)

    4. Degeneration of nerve cells (poultry)

    • Vascular System: Hemolysis of red blood cells.

    • Reproductive System:

    • Males: Inhibition of spermatogenesis.

    • Females: Fetal resorption (degeneration).

Requirements of Vitamin E

  • Affected by intake of:

    1. Selenium

    2. Unsaturated fatty acids

    3. Synthetic antioxidants (such as ethoxyquin, BHA, BHT)

    4. Tissue reserves of vitamin E

Vitamin E Deficiency in Cats: Pansteatitis

  • Yellow fat disease characterized by inflammation and yellow-brown discoloration of body fat.

  • Signs of deficiency:

    • Depression, anorexia

    • Hyperesthesia (sensitivity to touch) of the chest and abdomen

    • Reluctance to move, decreased agility

    • Presence of abnormal fat deposits under the skin and in the abdomen

    • Dietary history includes items high in unsaturated fats and low in vitamin E.

Treatment of Vitamin E Deficiency in Cats

  • Elimination of fish from the cat’s diet.

  • Replacement with well-balanced, high-quality commercial cat food.

  • Administration of vitamin E (α-tocopherol) orally at 10 to 25 IU twice daily for 5-7 days.

Vitamin E Toxicity

  • Not a practical problem; it is one of the least toxic vitamins.

  • Doses of 1,000 to 2,000 IU/kg of diet have not shown adverse effects.

  • In humans, oral doses as large as 3,200 IU did not lead to detrimental effects.

Vitamin K

  • Discovered in 1929 with cholesterol-depletion studies in chicks.

  • Synthesized by bacteria in the digestive tract.

  • Has the least amount of storage in the body among fat-soluble vitamins.

Chemical Forms of Vitamin K

  • Represents a group of vitamers:

    1. Vitamin K1 (phylloquinone) – natural source found in green vegetables.

    2. Vitamin K2 (menaquinone) – natural source produced by enteric bacteria.

    3. Vitamin K3 (menadione) – synthetic source, most potent and water-soluble of the three forms.

Functions of Vitamin K

  • Involved in blood coagulation.

  • Coagulation Proteins (liver):

    • Factor II (prothrombin)

    • Factor VII (proconvertin)

    • Factor IX (Christmas factor)

    • Factor X (Stuart-Prower factor)

  • Abnormal prothrombin (Factor II) is produced in cases of:

    • Deficiency of vitamin K

    • Presence of a competitive inhibitor

    • Anti-vitamins such as dicoumarol and warfarin, which prevent prothrombin synthesis by the liver.

Sweet Clover Disease and Warfarin

  • Dicoumarol & Warfarin:

    • Both prevent synthesis of prothrombin by the liver; serve as anti-vitamins.

International Units of Vitamin K

  • Menadione is the reference standard.

  • One IU of vitamin K activity = 1 µg of menadione; biological assay is based on clotting time in young chicks.

Factors Affecting Vitamin K Requirements

  1. Bioavailability of vitamin K in various ingredients.

  2. Level of dietary fat.

  3. Use of antibiotics.

  4. Microbial synthesis in the digestive tract (hindgut and rumen).

  5. Exposure and consumption of feces (coprophagy).

Natural Sources of Vitamin K

  • Green leafy vegetables

  • Eggs

  • Liver

  • Fish meal

Dietary Supplementation with Vitamin K

  • Menadione:

    • Pure vitamin K3 is a crystalline yellow powder, unstable, and can irritate skin and mucous membranes.

    • Can be complexed to improve stability and safety, including:

    • Menadione sodium bisulfite (MSB)

    • Menadione sodium bisulfite complex (MSBC)

    • Menadione nicotinamide bisulfite (MNB)

    • Menadione dimethyl pyrimidinol bisulfate (MPB)

Vitamin K Toxicity

  • High concentrations of menadione compounds are well-tolerated by animals.

  • Studies with pigs and young chickens (e.g., 110 mg/kg for pigs and 300 mg/kg for young chickens) showed no signs of toxicity.

Water-Soluble Vitamins

The B-Vitamins

  1. Thiamin (vitamin B1)

  2. Riboflavin (vitamin B2)

  3. Niacin (vitamin B3)

  4. Pantothenic acid (pantothenate)

  5. Vitamin B6 (pyridoxine)

  6. Biotin

  7. Folate (folic acid)

  8. Vitamin B12

Thiamin (Vitamin B1)

  • First of the water-soluble vitamins discovered.

  • Unstable when exposed to UV light.

  • Reacts strongly in Maillard-type reactions.

  • Originally named "thio-amine."

Functions of Thiamin

  • Thiamin pyrophosphate (TPP) is a coenzyme:

    • Involved in decarboxylation of $ ext{α-keto}$ acids.

    • One of five coenzymes required for proper pyruvate dehydrogenase activity.

Thiamin in Metabolism

  • Important for many metabolic pathways including the citric acid cycle (TCA or Krebs cycle), glycolysis, gluconeogenesis, amino acid metabolism, and fatty acid synthesis.

    • Example Reactions:

    • $ ext{pyruvate} + ext{TPP}
      ightarrow ext{acetyl CoA}$

    • $ ext{succinyl-CoA} + ext{α-ketoglutarate dehydrogenase}
      ightarrow ext{α-ketoglutarate}$.

Sources of Thiamin

  • Yeast, yeast extracts, pork (highest levels).

  • Cereal grains (whole grains better than refined products) found primarily in the outer hull.

  • In the U.S., processed flour is required to be fortified with thiamin mononitrate, niacin, riboflavin, folic acid, and iron (ferrous).

Thiamin Deficiency Symptoms

  • Common in regions with polished rice diets where husks are removed.

    • Beriberi (in humans):

    • Dry beriberi: Wasting and partial paralysis due to peripheral nerve damage.

    • Wet beriberi: Weakening of capillary walls of the heart causing edema in peripheral tissues.

  • Polyneuritis in poultry (counterpart to beriberi) includes:

    • Anorexia, cardiac enlargement, muscular weakness.

Riboflavin (Vitamin B2)

  • The name riboflavin derives from "ribo" (ribose) and "flavin" (yellow).

  • Imparts yellow color on vitamin premixes.

  • Fun fact: consumption of pure riboflavin turns urine fluorescent yellow.

Functions of Riboflavin

  • Component of flavoproteins and coenzymes:

    • Flavin mononucleotide (FMN)

    • Flavin adenine dinucleotide (FAD).

  • Important in oxidation-reduction reactions and in the electron transport chain within the mitochondria.

Sources of Riboflavin

  • Cereal grains are poor sources, supplementation is necessary.

  • Good sources include: yeast, liver, milk, and green leafy vegetables.

Riboflavin Deficiency Symptoms

  • Most common dietary deficiency but rarely shows deficiency symptoms.

  • General symptoms include:

    • Poor growth, diarrhea (secondary due to impaired nutrient absorption), eye abnormalities, hair loss, and dermatitis.

  • Specific symptoms:

    • "Curled toe paralysis" in young chickens due to peripheral nerve degeneration.

Niacin (Vitamin B3)

  • First described in 1873 in studies on nicotine.

  • Active form is nicotinamide.

Functions of Niacin

  • Component of 2 coenzymes:

    • NAD (nicotinamide adenine dinucleotide)

    • NADP (phosphorylated NAD), which over 200 enzymes require.

  • Involved in carbohydrate, lipid, and amino acid metabolism.

Niacin and Tryptophan Linkage

  • Niacin can be synthesized from tryptophan; however, conversion rate is slow (60-to-1).

  • Dietary sources and supplementation are still necessary.

Sources of Niacin

  • Animal proteins (such as beef, eggs, milk) are good sources providing "niacin equivalents" (preformed niacin + tryptophan).

  • Corn is low in niacin and tryptophan and contains niacinogen (binds niacin).

  • Generally, cereal grains contain niacin-carbohydrate or niacin-protein complexes; niacin is 80-90% available in this form, referred to as nyacitin.

Niacin Deficiency Symptoms

  • General symptoms:

    • Poor growth and diarrhea (secondary due to impaired absorption).

  • Specific deficiency condition:

    • Pellagra in humans: known as the “disease of 4 D’s” (Diarrhea, Dermatitis, Dementia, Death).

  • Also characterized by hair loss, dermatitis (''necklace'' lesions), and known as “black tongue” in dogs.

Lipid-Modifying Effects of Niacin

  • At high doses (1,000 - 2,000 mg), niacin can reverse atherosclerosis by reducing cholesterol, TAG, VLDL, and LDL.

  • Daily doses of 1.5 - 6.0 g can lead to toxicity with symptoms such as:

    • Skin flushing, dry skin/rashes (e.g., eczema), maculopathy (thickening of macula and retina), acute toxic reactions.

Pantothenic Acid

  • Name derives from ‘pantothen’ (Greek: “from everywhere”).

  • Stable and usually occurs in bound form (acetyl CoA and acyl carrier protein).

Functions of Pantothenic Acid

  • Required for synthesis of coenzyme A (CoA).

  • Major role in the metabolism of fatty acids and carbohydrates.

  • Involved in addition and loss of 2 carbon units (acyl group transfer).

  • Component of fatty acid synthase, required for synthesis of fatty acids, cholesterol, and acetylcholine.

Sources of Pantothenic Acid

  • Found in most foods/feeds such as liver (especially chicken and pork), heart, egg yolk, yeast, molasses, whole grains, and wheat bran.

Pantothenic Acid Deficiency Symptoms

  • General symptoms (not specific):

    • Poor growth with secondary diarrhea, dermatitis, and hair loss (alopecia).

  • Chickens are the most susceptible to deficiency.

  • Symptoms such as "goose-stepping" gait in pigs and other nervous system disorders.

Vitamin B6 (Pyridoxine)

  • A generic descriptor for three forms:

    • Pyridoxine, pyridoxamine, pyridoxal.

  • The metabolically active form is pyridoxal phosphate.

Functions of Vitamin B6

  • Acts as coenzyme in macronutrient metabolism:

    • Decarboxylation, transamination, and racemization reactions.

    • Synthesis of neurotransmitters (e.g., serotonin, epi-/norepinephrine), histamine, hemoglobin, and participation in amino acid catabolism and gluconeogenesis.

Sources of Vitamin B6

  • Found in virtually all foods, including yeast, liver, milk, legumes, and cereal grains.

  • Forms: Plant sources (pyridoxine) are stable; animal sources (pyridoxal and pyridoxamine) are less stable.

  • Commercial forms include pyridoxine HCl, which is very stable.

Vitamin B6 Deficiency Symptoms

  • General symptoms (not specific):

    • Poor growth rate, scaling dermatitis, and hyperirritability.

  • Specific symptoms include muscular weakness and anemia, infertility, fetal malformations, and insulin insufficiency due to reduced pancreatic synthesis.

Biotin

  • Free biotin is not very stable.

  • Found in ingredients as biocytin (amide complex of biotin and lysine).

Functions of Biotin

  • Essential component of specific carboxylase enzymes.

  • Involved in both carboxylation and decarboxylation reactions; most functions occur in the mitochondria.

Sources of Biotin

  • Few foods/feeds are good sources; animal products and fermentation by-products include egg yolk, yeast, milk, kidney, and liver.

  • Plant sources such as oilseed meals (e.g., soybean meal) are available but vary widely in bioavailability.

Biotin–Avidin Interaction

  • Avidin (glycoprotein secreted by the hen's oviduct) binds to biotin forming a complex.

  • The complex cannot be hydrolyzed by body enzymes; however, cooking breaks the bond.

  • Biotin is also present in unbound form in egg yolk.

Biotin Deficiency Symptoms

  • General symptoms: poor growth, dermatitis, and hair loss (alopecia).

  • Symptoms may also include impaired lipid and energy metabolism and cracked pads on feet.

Folic Acid (Folate)

  • Name derives from Latin ‘folium’, meaning “leaf.”

  • Exists in various forms: free folate, dihydrofolate (DHF), tetrahydrofolate (THF).

Functions of Folic Acid

  1. Carrier of methyl groups that are added to or removed from amino acids (e.g., His, Ser, Met), purines, and polyamines.

  2. Tetrahydrofolate is essential for the synthesis of thymidylic acid (thymine, DNA).

  3. Important in purine synthesis (adenine and guanine).

  4. Initiation of translation (protein synthesis) with formylmethionine.

Sources of Folic Acid

  • Found in green leafy materials, cereal grains, extracted oilseed meals, and animal protein meals.

  • Good sources: liver (beef and chicken) and brewer's yeast.

  • Important to note that processing may remove folic acid from cereal grains; mandatory fortification began in the U.S. in 1996 (e.g., in breads, cereals, flours, and pastas).

Folic Acid Deficiency Symptoms

  • Results in reduced biosynthesis of DNA and RNA, leading to reduced cell division.

  • Particularly important for women of child-bearing age; supplementation must occur before pregnancy to prevent neural tube defects.

Vitamin B12

  • Also known as cobalamin; imparts a deep red color.

  • Comprises classes of vitamers, including methylcobalamin and adenosylcobalamin.

Characteristics of Vitamin B12

  • Not synthesized by plants or animals; synthesized by a few microorganisms (bacteria, yeasts, or algae).

  • Cobalt is necessary for synthesis (forms part of the structure).

Vitamin B12 Sources

  • Good sources include meat and bone meal, fish meal, and whey.

  • Ruminants use dietary cobalt for B12 synthesis; non-ruminants do not require cobalt, only B12, leading to potential deficiencies on vegetarian or vegan diets.

Functions of Vitamin B12

  1. Synthesis of labile methyl groups.

    • B12 is the coenzyme for methionine synthase, a methyltransferase enzyme.

    • Lack of B12 causes pernicious anemia due to a lack of mature RBCs, limited DNA synthesis, and impaired oxygen transport.

  2. Glucose synthesis, especially vital in ruminants through methylmalonyl-CoA mutase.

Deficiency Symptoms of Vitamin B12

  • Ruminants may experience deficiencies induced by low cobalt levels.

  • General symptoms include: weight loss, wasting, listlessness, mild anemia, decreased growth/feed intake, nervous system disorders (e.g., uncoordinated posture), and increased fat deposition in liver, heart, and kidneys.

Vitamin C (Ascorbic Acid)

  • Chemical Formula:

    • HO

    • HO

    • CHO

    • HO

    • OH

  • Dietary Requirement:

    • Only primates (including humans) and guinea pigs, along with some specific animal species (e.g., red-vented bulbul bird, fruit bat) have a dietary requirement for vitamin C due to lack of $ ext{L-gulonolactone oxidase}$.

Characteristics of Vitamin C

  • Present in reduced form in foods and very soluble in water.

  • Easily destroyed by oxidation due to heat, air exposure, and presence of minerals or oxidative enzymes.

  • Limited storage in the body; needs to be regularly provided via diet and is essentially non-toxic.

Functions of Vitamin C

  1. Formation of collagen (as a catalyst); collagen requires synthesis of hydroxyproline from proline.

    • Important for connective tissues (bone, teeth, cartilage, tendons, ligaments, fibrous matrices of skin and blood vessels).

  2. Acts as a water-soluble antioxidant.

  3. Increases absorption of non-heme iron by reducing it from $ ext{Fe}^{3+}$ to $ ext{Fe}^{2+}$.

Deficiency Symptoms of Vitamin C

  1. Scurvy:

    • Characterized by fragile capillaries leading to hemorrhage; swollen, bleeding and ulcerated gums; loose teeth; skin lesions; and weak bones.

  2. Anemia can occur due to impaired activation of folic acid and reduced dietary iron absorption.

Sources of Vitamin C

  • Citrus fruits and many vegetables (e.g., bell pepper, strawberries, and oranges) are good sources.

Benefits of Vitamin C for Livestock Species

  • Supplementation shown to improve growth, egg production, feed efficiency, egg weight, shell quality, and livability during heat stress (200-600 mg/kg diet).

Quasi-Vitamins

  • Other compounds have been proposed as vitamins, fitting the vitamin designation for specific animal species, indicating that the full list of vitamins may not be complete.

Examples of Quasi-Vitamins

  • Ubiquinone

  • p-Aminobenzoic acid

  • Lipoic acid

  • Allyl sulfur compounds

  • Flavonoids and polyphenols

  • Glucosinolates

  • Phytoestrogens

  • Choline

  • Taurine

  • Carnitine

  • Inositol

  • Pyrroloquinoline quinone

  • Orotic Acid

Choline

  • Discovered in 1864, chemically synthesized in 1866.

  • Classified as an essential nutrient for humans in 1998; chemically, a quaternary saturated amine usually fed as choline chloride (animal nutrition) or choline bitartrate (human nutrition).

  • Natural source is phosphatidylcholine (lecithin), enriched in soy-based ingredients.

Functions of Choline

  • Component of phospholipids, affecting structural integrity, membrane fluidity, and signaling roles in cell membranes.

Choline Metabolism

  • Methylation of phosphatidylethanolamine.

  • Dietary requirement influenced by dietary intake of methionine; chickens have a much higher requirement for preformed choline due to lack of the methylation enzyme.

Choline Deficiency Symptoms

  • Deficiency is rare due to widespread distribution in foods/feeds and the capacity for endogenous synthesis from methionine.

  • Can occur in young birds fed low-choline diets, leading to:

    • Slow growth, fatty liver infiltration, lack of coordination, and low conception rates.

Taurine

  • Often misnamed an 'amino acid' but is technically a β-amino sulfonic acid and is not incorporated into proteins.

  • Functions:

    • Important for visual acuity, neurodevelopment, calcium regulation, antioxidant activity, bile acid conjugation.

Natural Sources of Taurine

  • Seafood and meat are key sources; taurine is a major constituent of bile.

Taurine Deficiency in Cats

  • Cats cannot synthesize taurine; deficiencies lead to:

    • Central retinal degeneration (CRD) and feline dilated cardiomyopathy.

    • Inclusion in feline diets is mandated by the Association of American Feed Control Officials (AAFCO).

Take-Home Messages

  • Vitamins are essential nutrients that must be ingested in minute concentrations to maintain metabolic, physiologic, and immune function.

  • All vitamins are composed of organic elements, some including inorganic mineral elements in their structure.

  • Fat-soluble vitamins can be stored in the body, decreasing deficiency risk but increasing toxicity risk.

  • Water-soluble vitamins cannot be stored; excess intake is excreted by the kidneys.

  • Chemical synthesis of vitamins allows for easy dietary supplementation, disregarding natural vitamin activity.

  • Extreme variability exists in the concentration, form, and bioavailability of vitamins in natural ingredients.

  • Destruction of vitamin activity can occur from heat, oxygen exposure, sunlight, and poor storage conditions.

  • Inclusion of vitamin premixes is standard in nutrition practices but poses challenges in retaining vitamin activity.